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 $246.72   8.345%   $267.3088   $267.31   $267.30   $267.30  
  Purchase #2 $99.83   11.260%   $111.0709   $111.07   $111.05   $111.10  
  Purchase #3 $29.78   11.110%   $33.0886   $33.09   $33.10   $33.10  
  Purchase #4 $106.37   3.862%   $110.478   $110.48   $110.50   $110.50  
  Purchase #5 $19.91   5.163%   $20.938   $20.94   $20.95   $20.90  
  Purchase #6 $64.94   6.186%   $68.9572   $68.96   $68.95   $69.00  
  Purchase #7 $104.99   10.316%   $115.8208   $115.82   $115.80   $115.80  
  7 purchase totals = $672.54       $727.6623   $727.67   $727.65   $727.70