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 $183.88   11.766%   $205.5153   $205.52   $205.50   $205.50  
  Purchase #2 $247.38   10.207%   $272.6301   $272.63   $272.65   $272.60  
  Purchase #3 $27.61   8.482%   $29.9519   $29.95   $29.95   $30.00  
  Purchase #4 $75.25   9.380%   $82.3085   $82.31   $82.30   $82.30  
  Purchase #5 $222.71   3.419%   $230.3245   $230.32   $230.30   $230.30  
  Purchase #6 $10.27   9.382%   $11.2335   $11.23   $11.25   $11.20  
  Purchase #7 $187.33   3.618%   $194.1076   $194.11   $194.10   $194.10  
  7 purchase totals = $954.43       $1,026.0714   $1,026.07   $1,026.05   $1,026.00