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 $190.84   6.764%   $203.7484   $203.75   $203.75   $203.70  
  Purchase #2 $109.62   13.628%   $124.559   $124.56   $124.55   $124.60  
  Purchase #3 $190.90   8.786%   $207.6725   $207.67   $207.65   $207.70  
  Purchase #4 $104.32   11.763%   $116.5912   $116.59   $116.60   $116.60  
  Purchase #5 $104.79   8.193%   $113.3754   $113.38   $113.40   $113.40  
  Purchase #6 $109.78   4.765%   $115.011   $115.01   $115.00   $115.00  
  Purchase #7 $48.37   8.832%   $52.642   $52.64   $52.65   $52.60  
  7 purchase totals = $858.62       $933.5995   $933.60   $933.60   $933.60