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 $63.95   9.504%   $70.0278   $70.03   $70.05   $70.00  
  Purchase #2 $68.27   10.535%   $75.4622   $75.46   $75.45   $75.50  
  Purchase #3 $239.82   4.834%   $251.4129   $251.41   $251.40   $251.40  
  Purchase #4 $13.95   13.527%   $15.837   $15.84   $15.85   $15.80  
  Purchase #5 $87.97   12.630%   $99.0806   $99.08   $99.10   $99.10  
  Purchase #6 $244.79   4.197%   $255.0638   $255.06   $255.05   $255.10  
  Purchase #7 $41.89   8.322%   $45.3761   $45.38   $45.40   $45.40  
  7 purchase totals = $760.64       $812.2604   $812.26   $812.30   $812.30