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 $208.59   5.742%   $220.5672   $220.57   $220.55   $220.60  
  Purchase #2 $225.37   11.237%   $250.6948   $250.69   $250.70   $250.70  
  Purchase #3 $203.79   6.339%   $216.7082   $216.71   $216.70   $216.70  
  Purchase #4 $93.95   3.721%   $97.4459   $97.45   $97.45   $97.40  
  Purchase #5 $13.48   3.843%   $13.998   $14.00   $14.00   $14.00  
  Purchase #6 $11.85   7.439%   $12.7315   $12.73   $12.75   $12.70  
  Purchase #7 $64.94   5.810%   $68.713   $68.71   $68.70   $68.70  
  7 purchase totals = $821.97       $880.8586   $880.86   $880.85   $880.80