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 $62.88   5.482%   $66.3271   $66.33   $66.35   $66.30  
  Purchase #2 $139.33   11.122%   $154.8263   $154.83   $154.85   $154.80  
  Purchase #3 $190.63   9.737%   $209.1916   $209.19   $209.20   $209.20  
  Purchase #4 $198.78   7.753%   $214.1914   $214.19   $214.20   $214.20  
  Purchase #5 $27.62   11.628%   $30.8317   $30.83   $30.85   $30.80  
  Purchase #6 $176.70   12.607%   $198.9766   $198.98   $199.00   $199.00  
  Purchase #7 $95.57   13.691%   $108.6545   $108.65   $108.65   $108.70  
  7 purchase totals = $891.51       $982.9992   $983.00   $983.10   $983.00