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 $88.64   7.468%   $95.2596   $95.26   $95.25   $95.30  
  Purchase #2 $154.51   3.305%   $159.6166   $159.62   $159.60   $159.60  
  Purchase #3 $45.62   7.461%   $49.0237   $49.02   $49.00   $49.00  
  Purchase #4 $29.64   5.764%   $31.3484   $31.35   $31.35   $31.30  
  Purchase #5 $250.38   6.426%   $266.4694   $266.47   $266.45   $266.50  
  Purchase #6 $156.52   9.678%   $171.668   $171.67   $171.65   $171.70  
  Purchase #7 $33.71   6.736%   $35.9807   $35.98   $36.00   $36.00  
  7 purchase totals = $759.02       $809.3664   $809.37   $809.30   $809.40