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 $68.76   9.274%   $75.1368   $75.14   $75.15   $75.10  
  Purchase #2 $87.71   3.406%   $90.6974   $90.70   $90.70   $90.70  
  Purchase #3 $81.73   7.356%   $87.7421   $87.74   $87.75   $87.70  
  Purchase #4 $248.40   7.527%   $267.0971   $267.10   $267.10   $267.10  
  Purchase #5 $190.29   9.503%   $208.3733   $208.37   $208.35   $208.40  
  Purchase #6 $215.34   9.552%   $235.9093   $235.91   $235.90   $235.90  
  Purchase #7 $105.77   13.207%   $119.739   $119.74   $119.75   $119.70  
  7 purchase totals = $998.00       $1,084.6950   $1,084.70   $1,084.70   $1,084.60