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 $210.76   11.249%   $234.4684   $234.47   $234.45   $234.50  
  Purchase #2 $15.69   12.141%   $17.5949   $17.59   $17.60   $17.60  
  Purchase #3 $243.70   3.103%   $251.262   $251.26   $251.25   $251.30  
  Purchase #4 $91.29   6.315%   $97.055   $97.06   $97.05   $97.10  
  Purchase #5 $158.27   4.873%   $165.9825   $165.98   $166.00   $166.00  
  Purchase #6 $200.73   7.734%   $216.2545   $216.25   $216.25   $216.30  
  Purchase #7 $62.71   12.865%   $70.7776   $70.78   $70.80   $70.80  
  7 purchase totals = $983.15       $1,053.3949   $1,053.39   $1,053.40   $1,053.60