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 $197.63   13.817%   $224.9365   $224.94   $224.95   $224.90  
  Purchase #2 $15.57   12.155%   $17.4625   $17.46   $17.45   $17.50  
  Purchase #3 $81.82   4.822%   $85.7654   $85.77   $85.75   $85.80  
  Purchase #4 $216.38   7.617%   $232.8617   $232.86   $232.85   $232.90  
  Purchase #5 $96.41   4.567%   $100.813   $100.81   $100.80   $100.80  
  Purchase #6 $225.41   6.226%   $239.444   $239.44   $239.45   $239.40  
  Purchase #7 $189.31   4.247%   $197.35   $197.35   $197.35   $197.40  
  7 purchase totals = $1,022.53       $1,098.6331   $1,098.63   $1,098.60   $1,098.70