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 $175.71   10.623%   $194.3757   $194.38   $194.40   $194.40  
  Purchase #2 $239.47   12.181%   $268.6398   $268.64   $268.65   $268.60  
  Purchase #3 $37.27   10.801%   $41.2955   $41.30   $41.30   $41.30  
  Purchase #4 $226.87   8.160%   $245.3826   $245.38   $245.40   $245.40  
  Purchase #5 $230.62   7.621%   $248.1956   $248.20   $248.20   $248.20  
  Purchase #6 $61.89   3.547%   $64.0852   $64.09   $64.10   $64.10  
  Purchase #7 $222.31   3.271%   $229.5818   $229.58   $229.60   $229.60  
  7 purchase totals = $1,194.14       $1,291.5562   $1,291.57   $1,291.65   $1,291.60