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 $204.39   13.339%   $231.6536   $231.65   $231.65   $231.70  
  Purchase #2 $181.83   6.709%   $194.029   $194.03   $194.05   $194.00  
  Purchase #3 $18.69   13.281%   $21.1722   $21.17   $21.15   $21.20  
  Purchase #4 $181.39   5.517%   $191.3973   $191.40   $191.40   $191.40  
  Purchase #5 $159.79   8.430%   $173.2603   $173.26   $173.25   $173.30  
  Purchase #6 $171.87   13.709%   $195.4317   $195.43   $195.45   $195.40  
  Purchase #7 $190.52   5.462%   $200.9262   $200.93   $200.95   $200.90  
  7 purchase totals = $1,108.48       $1,207.8703   $1,207.87   $1,207.90   $1,207.90