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 $84.55   12.286%   $94.9378   $94.94   $94.95   $94.90  
  Purchase #2 $177.49   9.805%   $194.8929   $194.89   $194.90   $194.90  
  Purchase #3 $180.84   8.731%   $196.6291   $196.63   $196.65   $196.60  
  Purchase #4 $69.60   11.407%   $77.5393   $77.54   $77.55   $77.50  
  Purchase #5 $25.69   7.522%   $27.6224   $27.62   $27.60   $27.60  
  Purchase #6 $121.62   11.457%   $135.554   $135.55   $135.55   $135.60  
  Purchase #7 $143.28   9.204%   $156.4675   $156.47   $156.45   $156.50  
  7 purchase totals = $803.07       $883.6430   $883.64   $883.65   $883.60