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 $61.28   3.219%   $63.2526   $63.25   $63.25   $63.30  
  Purchase #2 $117.90   7.193%   $126.3805   $126.38   $126.40   $126.40  
  Purchase #3 $114.31   6.726%   $121.9985   $122.00   $122.00   $122.00  
  Purchase #4 $84.33   3.809%   $87.5421   $87.54   $87.55   $87.50  
  Purchase #5 $186.63   12.709%   $210.3488   $210.35   $210.35   $210.30  
  Purchase #6 $166.76   11.707%   $186.2826   $186.28   $186.30   $186.30  
  Purchase #7 $138.98   4.339%   $145.0103   $145.01   $145.00   $145.00  
  7 purchase totals = $870.19       $940.8154   $940.81   $940.85   $940.80