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 $62.28   8.387%   $67.5034   $67.50   $67.50   $67.50  
  Purchase #2 $245.31   13.297%   $277.9289   $277.93   $277.95   $277.90  
  Purchase #3 $157.31   10.607%   $173.9959   $174.00   $174.00   $174.00  
  Purchase #4 $125.92   7.763%   $135.6952   $135.70   $135.70   $135.70  
  Purchase #5 $180.93   11.180%   $201.158   $201.16   $201.15   $201.20  
  Purchase #6 $108.54   12.380%   $121.9773   $121.98   $122.00   $122.00  
  Purchase #7 $222.32   13.326%   $251.9464   $251.95   $251.95   $251.90  
  7 purchase totals = $1,102.61       $1,230.2051   $1,230.22   $1,230.25   $1,230.20