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 $213.44   6.483%   $227.2773   $227.28   $227.30   $227.30  
  Purchase #2 $49.55   12.599%   $55.7928   $55.79   $55.80   $55.80  
  Purchase #3 $171.76   3.600%   $177.9434   $177.94   $177.95   $177.90  
  Purchase #4 $62.49   11.361%   $69.5895   $69.59   $69.60   $69.60  
  Purchase #5 $99.27   8.278%   $107.4876   $107.49   $107.50   $107.50  
  Purchase #6 $19.90   13.761%   $22.6384   $22.64   $22.65   $22.60  
  Purchase #7 $96.64   3.781%   $100.294   $100.29   $100.30   $100.30  
  7 purchase totals = $713.05       $761.0230   $761.02   $761.10   $761.00