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 $55.92   6.765%   $59.703   $59.70   $59.70   $59.70  
  Purchase #2 $51.48   7.170%   $55.1711   $55.17   $55.15   $55.20  
  Purchase #3 $200.26   10.364%   $221.0149   $221.01   $221.00   $221.00  
  Purchase #4 $224.63   11.816%   $251.1723   $251.17   $251.15   $251.20  
  Purchase #5 $59.43   4.565%   $62.143   $62.14   $62.15   $62.10  
  Purchase #6 $188.41   13.671%   $214.1675   $214.17   $214.15   $214.20  
  Purchase #7 $238.98   13.844%   $272.0644   $272.06   $272.05   $272.10  
  7 purchase totals = $1,019.11       $1,135.4362   $1,135.42   $1,135.35   $1,135.50