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 $196.87   10.230%   $217.0098   $217.01   $217.00   $217.00  
  Purchase #2 $225.56   12.409%   $253.5497   $253.55   $253.55   $253.50  
  Purchase #3 $95.92   6.843%   $102.4838   $102.48   $102.50   $102.50  
  Purchase #4 $200.37   10.452%   $221.3127   $221.31   $221.30   $221.30  
  Purchase #5 $44.61   10.131%   $49.1294   $49.13   $49.15   $49.10  
  Purchase #6 $64.38   6.318%   $68.4475   $68.45   $68.45   $68.40  
  Purchase #7 $220.70   8.743%   $239.9958   $240.00   $240.00   $240.00  
  7 purchase totals = $1,048.41       $1,151.9287   $1,151.93   $1,151.95   $1,151.80