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 $52.71   4.484%   $55.0735   $55.07   $55.05   $55.10  
  Purchase #2 $163.37   5.675%   $172.6412   $172.64   $172.65   $172.60  
  Purchase #3 $104.65   12.681%   $117.9207   $117.92   $117.90   $117.90  
  Purchase #4 $119.80   5.405%   $126.2752   $126.28   $126.30   $126.30  
  Purchase #5 $199.29   6.593%   $212.4292   $212.43   $212.45   $212.40  
  Purchase #6 $61.65   9.226%   $67.3378   $67.34   $67.35   $67.30  
  Purchase #7 $159.77   9.611%   $175.1255   $175.13   $175.15   $175.10  
  7 purchase totals = $861.24       $926.8031   $926.81   $926.85   $926.70