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 $68.99   4.781%   $72.2884   $72.29   $72.30   $72.30  
  Purchase #2 $129.62   3.392%   $134.0167   $134.02   $134.00   $134.00  
  Purchase #3 $21.63   7.791%   $23.3152   $23.32   $23.30   $23.30  
  Purchase #4 $199.37   5.689%   $210.7122   $210.71   $210.70   $210.70  
  Purchase #5 $116.32   6.428%   $123.797   $123.80   $123.80   $123.80  
  Purchase #6 $100.92   5.868%   $106.842   $106.84   $106.85   $106.80  
  Purchase #7 $69.98   9.804%   $76.8408   $76.84   $76.85   $76.80  
  7 purchase totals = $706.83       $747.8123   $747.82   $747.80   $747.70