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 $52.60   8.771%   $57.2135   $57.21   $57.20   $57.20  
  Purchase #2 $191.81   6.809%   $204.8703   $204.87   $204.85   $204.90  
  Purchase #3 $16.95   9.507%   $18.5614   $18.56   $18.55   $18.60  
  Purchase #4 $121.73   6.695%   $129.8798   $129.88   $129.90   $129.90  
  Purchase #5 $61.69   8.424%   $66.8868   $66.89   $66.90   $66.90  
  Purchase #6 $28.84   6.250%   $30.6425   $30.64   $30.65   $30.60  
  Purchase #7 $50.91   9.279%   $55.6339   $55.63   $55.65   $55.60  
  7 purchase totals = $524.53       $563.6882   $563.68   $563.70   $563.70