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 $87.86   8.808%   $95.5987   $95.60   $95.60   $95.60  
  Purchase #2 $229.97   3.538%   $238.1063   $238.11   $238.10   $238.10  
  Purchase #3 $106.60   8.682%   $115.855   $115.86   $115.85   $115.90  
  Purchase #4 $19.53   7.294%   $20.9545   $20.95   $20.95   $21.00  
  Purchase #5 $88.88   5.746%   $93.987   $93.99   $94.00   $94.00  
  Purchase #6 $201.96   4.183%   $210.408   $210.41   $210.40   $210.40  
  Purchase #7 $228.69   7.485%   $245.8074   $245.81   $245.80   $245.80  
  7 purchase totals = $963.49       $1,020.7169   $1,020.73   $1,020.70   $1,020.80