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 $66.62   7.596%   $71.6805   $71.68   $71.70   $71.70  
  Purchase #2 $112.27   6.499%   $119.5664   $119.57   $119.55   $119.60  
  Purchase #3 $206.59   10.118%   $227.4928   $227.49   $227.50   $227.50  
  Purchase #4 $182.48   12.312%   $204.9469   $204.95   $204.95   $204.90  
  Purchase #5 $108.93   13.631%   $123.7782   $123.78   $123.80   $123.80  
  Purchase #6 $25.27   6.638%   $26.9474   $26.95   $26.95   $26.90  
  Purchase #7 $142.79   13.121%   $161.5255   $161.53   $161.55   $161.50  
  7 purchase totals = $844.95       $935.9377   $935.95   $936.00   $935.90