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 $187.82   7.635%   $202.1601   $202.16   $202.15   $202.20  
  Purchase #2 $163.68   6.514%   $174.3421   $174.34   $174.35   $174.30  
  Purchase #3 $92.71   10.465%   $102.4121   $102.41   $102.40   $102.40  
  Purchase #4 $207.91   13.281%   $235.5225   $235.52   $235.50   $235.50  
  Purchase #5 $30.76   10.509%   $33.9926   $33.99   $34.00   $34.00  
  Purchase #6 $183.71   10.332%   $202.6909   $202.69   $202.70   $202.70  
  Purchase #7 $46.76   9.105%   $51.0175   $51.02   $51.00   $51.00  
  7 purchase totals = $913.35       $1,002.1378   $1,002.13   $1,002.10   $1,002.10