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 $93.25   12.359%   $104.7748   $104.77   $104.75   $104.80  
  Purchase #2 $46.45   13.560%   $52.7486   $52.75   $52.75   $52.70  
  Purchase #3 $117.76   6.608%   $125.5416   $125.54   $125.55   $125.50  
  Purchase #4 $219.51   10.840%   $243.3049   $243.30   $243.30   $243.30  
  Purchase #5 $50.59   5.419%   $53.3315   $53.33   $53.35   $53.30  
  Purchase #6 $135.77   13.842%   $154.5633   $154.56   $154.55   $154.60  
  Purchase #7 $171.31   5.305%   $180.398   $180.40   $180.40   $180.40  
  7 purchase totals = $834.64       $914.6627   $914.65   $914.65   $914.60