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 $198.26   13.870%   $225.7587   $225.76   $225.75   $225.80  
  Purchase #2 $55.38   12.585%   $62.3496   $62.35   $62.35   $62.30  
  Purchase #3 $102.25   11.282%   $113.7858   $113.79   $113.80   $113.80  
  Purchase #4 $233.96   4.756%   $245.0871   $245.09   $245.10   $245.10  
  Purchase #5 $124.84   6.519%   $132.9783   $132.98   $133.00   $133.00  
  Purchase #6 $119.49   11.845%   $133.6436   $133.64   $133.65   $133.60  
  Purchase #7 $126.46   8.406%   $137.0902   $137.09   $137.10   $137.10  
  7 purchase totals = $960.64       $1,050.6933   $1,050.70   $1,050.75   $1,050.70