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 $56.46   10.831%   $62.5752   $62.58   $62.60   $62.60  
  Purchase #2 $81.70   6.474%   $86.9893   $86.99   $87.00   $87.00  
  Purchase #3 $210.45   12.334%   $236.4069   $236.41   $236.40   $236.40  
  Purchase #4 $175.88   5.677%   $185.8647   $185.86   $185.85   $185.90  
  Purchase #5 $98.58   3.872%   $102.397   $102.40   $102.40   $102.40  
  Purchase #6 $18.39   13.169%   $20.8118   $20.81   $20.80   $20.80  
  Purchase #7 $247.48   11.280%   $275.3957   $275.40   $275.40   $275.40  
  7 purchase totals = $888.94       $970.4406   $970.45   $970.45   $970.50