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 $57.54   4.806%   $60.3054   $60.31   $60.30   $60.30  
  Purchase #2 $110.82   5.497%   $116.9118   $116.91   $116.90   $116.90  
  Purchase #3 $145.36   3.682%   $150.7122   $150.71   $150.70   $150.70  
  Purchase #4 $56.60   7.845%   $61.0403   $61.04   $61.05   $61.00  
  Purchase #5 $135.25   7.118%   $144.8771   $144.88   $144.90   $144.90  
  Purchase #6 $25.54   4.782%   $26.7613   $26.76   $26.75   $26.80  
  Purchase #7 $206.37   9.169%   $225.2921   $225.29   $225.30   $225.30  
  7 purchase totals = $737.48       $785.9002   $785.90   $785.90   $785.90