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 $28.76   13.650%   $32.6857   $32.69   $32.70   $32.70  
  Purchase #2 $146.63   4.323%   $152.9688   $152.97   $152.95   $153.00  
  Purchase #3 $168.56   3.872%   $175.0866   $175.09   $175.10   $175.10  
  Purchase #4 $179.63   11.637%   $200.5335   $200.53   $200.55   $200.50  
  Purchase #5 $203.44   9.473%   $222.7119   $222.71   $222.70   $222.70  
  Purchase #6 $225.46   7.138%   $241.5533   $241.55   $241.55   $241.60  
  Purchase #7 $194.92   4.153%   $203.015   $203.02   $203.00   $203.00  
  7 purchase totals = $1,147.40       $1,228.5548   $1,228.56   $1,228.55   $1,228.60