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 $73.63   12.379%   $82.7447   $82.74   $82.75   $82.70  
  Purchase #2 $250.53   7.650%   $269.6955   $269.70   $269.70   $269.70  
  Purchase #3 $87.73   7.641%   $94.4334   $94.43   $94.45   $94.40  
  Purchase #4 $65.73   7.850%   $70.8898   $70.89   $70.90   $70.90  
  Purchase #5 $113.89   9.203%   $124.3713   $124.37   $124.35   $124.40  
  Purchase #6 $20.54   11.355%   $22.8723   $22.87   $22.85   $22.90  
  Purchase #7 $55.30   8.776%   $60.1531   $60.15   $60.15   $60.20  
  7 purchase totals = $667.35       $725.1601   $725.15   $725.15   $725.20