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 $53.62   7.478%   $57.6297   $57.63   $57.65   $57.60  
  Purchase #2 $60.39   12.605%   $68.0022   $68.00   $68.00   $68.00  
  Purchase #3 $216.56   13.569%   $245.945   $245.95   $245.95   $245.90  
  Purchase #4 $29.76   13.794%   $33.8651   $33.87   $33.85   $33.90  
  Purchase #5 $44.60   3.424%   $46.1271   $46.13   $46.15   $46.10  
  Purchase #6 $211.57   13.284%   $239.675   $239.68   $239.70   $239.70  
  Purchase #7 $144.55   10.336%   $159.4907   $159.49   $159.50   $159.50  
  7 purchase totals = $761.05       $850.7348   $850.75   $850.80   $850.70