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 $84.77   11.421%   $94.4516   $94.45   $94.45   $94.50  
  Purchase #2 $75.71   8.184%   $81.9061   $81.91   $81.90   $81.90  
  Purchase #3 $120.82   11.199%   $134.3506   $134.35   $134.35   $134.40  
  Purchase #4 $93.55   11.732%   $104.5253   $104.53   $104.55   $104.50  
  Purchase #5 $218.95   5.212%   $230.3617   $230.36   $230.35   $230.40  
  Purchase #6 $66.79   12.419%   $75.0847   $75.08   $75.10   $75.10  
  Purchase #7 $56.78   10.123%   $62.5278   $62.53   $62.55   $62.50  
  7 purchase totals = $717.37       $783.2078   $783.21   $783.25   $783.30