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 $82.54   13.565%   $93.7366   $93.74   $93.75   $93.70  
  Purchase #2 $30.74   9.532%   $33.6701   $33.67   $33.65   $33.70  
  Purchase #3 $101.50   3.291%   $104.8404   $104.84   $104.85   $104.80  
  Purchase #4 $170.73   6.552%   $181.9162   $181.92   $181.90   $181.90  
  Purchase #5 $108.76   7.113%   $116.4961   $116.50   $116.50   $116.50  
  Purchase #6 $126.76   6.619%   $135.1502   $135.15   $135.15   $135.20  
  Purchase #7 $8.72   7.342%   $9.3602   $9.36   $9.35   $9.40  
  7 purchase totals = $629.75       $675.1698   $675.18   $675.15   $675.20