Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $194.97   8.696%   $211.9246   $211.92   $211.90   $211.90  
  Purchase #2 $221.52   10.714%   $245.2537   $245.25   $245.25   $245.30  
  Purchase #3 $191.94   11.665%   $214.3298   $214.33   $214.35   $214.30  
  Purchase #4 $124.93   10.167%   $137.6316   $137.63   $137.65   $137.60  
  Purchase #5 $242.37   3.461%   $250.7584   $250.76   $250.75   $250.80  
  Purchase #6 $198.71   3.563%   $205.79   $205.79   $205.80   $205.80  
  Purchase #7 $212.97   8.121%   $230.2653   $230.27   $230.25   $230.30  
  7 purchase totals = $1,387.41       $1,495.9534   $1,495.95   $1,495.95   $1,496.00