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 $56.42   11.260%   $62.7729   $62.77   $62.75   $62.80  
  Purchase #2 $129.32   13.409%   $146.6605   $146.66   $146.65   $146.70  
  Purchase #3 $72.33   9.676%   $79.3287   $79.33   $79.35   $79.30  
  Purchase #4 $184.80   3.773%   $191.7725   $191.77   $191.75   $191.80  
  Purchase #5 $15.47   12.241%   $17.3637   $17.36   $17.35   $17.40  
  Purchase #6 $195.26   3.711%   $202.5061   $202.51   $202.50   $202.50  
  Purchase #7 $27.59   7.823%   $29.7484   $29.75   $29.75   $29.70  
  7 purchase totals = $681.19       $730.1528   $730.15   $730.10   $730.20