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 $139.33   5.297%   $146.7103   $146.71   $146.70   $146.70  
  Purchase #2 $21.31   4.198%   $22.2046   $22.20   $22.20   $22.20  
  Purchase #3 $83.47   3.647%   $86.5142   $86.51   $86.50   $86.50  
  Purchase #4 $47.40   12.436%   $53.2947   $53.29   $53.30   $53.30  
  Purchase #5 $203.35   11.441%   $226.6153   $226.62   $226.60   $226.60  
  Purchase #6 $112.99   11.515%   $126.0008   $126.00   $126.00   $126.00  
  Purchase #7 $218.32   8.607%   $237.1108   $237.11   $237.10   $237.10  
  7 purchase totals = $826.17       $898.4507   $898.44   $898.40   $898.40