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 $55.66   9.624%   $61.0167   $61.02   $61.00   $61.00  
  Purchase #2 $26.78   5.287%   $28.1959   $28.20   $28.20   $28.20  
  Purchase #3 $81.45   3.428%   $84.2421   $84.24   $84.25   $84.20  
  Purchase #4 $165.98   11.756%   $185.4926   $185.49   $185.50   $185.50  
  Purchase #5 $61.57   6.819%   $65.7685   $65.77   $65.75   $65.80  
  Purchase #6 $244.67   5.585%   $258.3348   $258.33   $258.35   $258.30  
  Purchase #7 $30.32   4.288%   $31.6201   $31.62   $31.60   $31.60  
  7 purchase totals = $666.43       $714.6707   $714.67   $714.65   $714.60