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 $58.51   12.820%   $66.011   $66.01   $66.00   $66.00  
  Purchase #2 $124.29   9.123%   $135.629   $135.63   $135.65   $135.60  
  Purchase #3 $227.61   9.763%   $249.8316   $249.83   $249.85   $249.80  
  Purchase #4 $141.26   7.370%   $151.6709   $151.67   $151.65   $151.70  
  Purchase #5 $97.95   4.539%   $102.396   $102.40   $102.40   $102.40  
  Purchase #6 $95.80   13.283%   $108.5251   $108.53   $108.55   $108.50  
  Purchase #7 $30.86   10.357%   $34.0562   $34.06   $34.05   $34.10  
  7 purchase totals = $776.28       $848.1198   $848.13   $848.15   $848.10