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 $146.65   4.862%   $153.7801   $153.78   $153.80   $153.80  
  Purchase #2 $59.73   8.278%   $64.6744   $64.67   $64.65   $64.70  
  Purchase #3 $139.89   10.355%   $154.3756   $154.38   $154.40   $154.40  
  Purchase #4 $236.49   3.717%   $245.2803   $245.28   $245.30   $245.30  
  Purchase #5 $174.46   5.855%   $184.6746   $184.67   $184.65   $184.70  
  Purchase #6 $187.71   7.496%   $201.7807   $201.78   $201.80   $201.80  
  Purchase #7 $143.99   4.374%   $150.2881   $150.29   $150.30   $150.30  
  7 purchase totals = $1,088.92       $1,154.8538   $1,154.85   $1,154.90   $1,155.00