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 $197.86   8.137%   $213.9599   $213.96   $213.95   $214.00  
  Purchase #2 $182.65   4.856%   $191.5195   $191.52   $191.50   $191.50  
  Purchase #3 $148.89   3.108%   $153.5175   $153.52   $153.50   $153.50  
  Purchase #4 $59.75   8.227%   $64.6656   $64.67   $64.65   $64.70  
  Purchase #5 $238.68   7.431%   $256.4163   $256.42   $256.40   $256.40  
  Purchase #6 $114.36   10.491%   $126.3575   $126.36   $126.35   $126.40  
  Purchase #7 $28.92   13.337%   $32.7771   $32.78   $32.80   $32.80  
  7 purchase totals = $971.11       $1,039.2134   $1,039.23   $1,039.15   $1,039.30