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 $219.26   12.327%   $246.2882   $246.29   $246.30   $246.30  
  Purchase #2 $156.43   11.713%   $174.7526   $174.75   $174.75   $174.80  
  Purchase #3 $200.82   8.504%   $217.8977   $217.90   $217.90   $217.90  
  Purchase #4 $68.96   10.525%   $76.218   $76.22   $76.20   $76.20  
  Purchase #5 $131.36   12.661%   $147.9915   $147.99   $148.00   $148.00  
  Purchase #6 $207.59   8.457%   $225.1459   $225.15   $225.15   $225.10  
  Purchase #7 $204.41   6.851%   $218.4141   $218.41   $218.40   $218.40  
  7 purchase totals = $1,188.83       $1,306.7080   $1,306.71   $1,306.70   $1,306.70