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 $55.76   9.785%   $61.2161   $61.22   $61.20   $61.20  
  Purchase #2 $101.91   5.324%   $107.3357   $107.34   $107.35   $107.30  
  Purchase #3 $55.95   3.488%   $57.9015   $57.90   $57.90   $57.90  
  Purchase #4 $218.77   7.867%   $235.9806   $235.98   $236.00   $236.00  
  Purchase #5 $145.74   4.397%   $152.1482   $152.15   $152.15   $152.10  
  Purchase #6 $231.31   5.776%   $244.6705   $244.67   $244.65   $244.70  
  Purchase #7 $6.82   4.307%   $7.1137   $7.11   $7.10   $7.10  
  7 purchase totals = $816.26       $866.3663   $866.37   $866.35   $866.30