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 $62.35   7.437%   $66.987   $66.99   $67.00   $67.00  
  Purchase #2 $49.36   12.139%   $55.3518   $55.35   $55.35   $55.40  
  Purchase #3 $18.56   3.579%   $19.2243   $19.22   $19.20   $19.20  
  Purchase #4 $204.49   11.175%   $227.3418   $227.34   $227.35   $227.30  
  Purchase #5 $74.48   6.785%   $79.5335   $79.53   $79.55   $79.50  
  Purchase #6 $89.67   5.675%   $94.7588   $94.76   $94.75   $94.80  
  Purchase #7 $145.43   6.870%   $155.421   $155.42   $155.40   $155.40  
  7 purchase totals = $644.34       $698.6182   $698.61   $698.60   $698.60