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 $222.30   8.844%   $241.9602   $241.96   $241.95   $242.00  
  Purchase #2 $198.94   11.865%   $222.5442   $222.54   $222.55   $222.50  
  Purchase #3 $70.53   8.560%   $76.5674   $76.57   $76.55   $76.60  
  Purchase #4 $152.87   13.600%   $173.6603   $173.66   $173.65   $173.70  
  Purchase #5 $86.64   11.450%   $96.5603   $96.56   $96.55   $96.60  
  Purchase #6 $148.62   6.590%   $158.4141   $158.41   $158.40   $158.40  
  Purchase #7 $59.60   6.344%   $63.381   $63.38   $63.40   $63.40  
  7 purchase totals = $939.50       $1,033.0875   $1,033.08   $1,033.05   $1,033.20