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 $58.82   4.194%   $61.2869   $61.29   $61.30   $61.30  
  Purchase #2 $105.79   5.862%   $111.9914   $111.99   $112.00   $112.00  
  Purchase #3 $240.63   13.299%   $272.6314   $272.63   $272.65   $272.60  
  Purchase #4 $48.98   11.435%   $54.5809   $54.58   $54.60   $54.60  
  Purchase #5 $177.92   3.395%   $183.9604   $183.96   $183.95   $184.00  
  Purchase #6 $110.53   4.690%   $115.7139   $115.71   $115.70   $115.70  
  Purchase #7 $209.25   3.764%   $217.1262   $217.13   $217.15   $217.10  
  7 purchase totals = $951.92       $1,017.2911   $1,017.29   $1,017.35   $1,017.30