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 $124.50   7.232%   $133.5038   $133.50   $133.50   $133.50  
  Purchase #2 $228.73   9.723%   $250.9694   $250.97   $250.95   $251.00  
  Purchase #3 $33.38   4.424%   $34.8567   $34.86   $34.85   $34.90  
  Purchase #4 $184.43   8.428%   $199.9738   $199.97   $199.95   $200.00  
  Purchase #5 $224.89   7.806%   $242.4449   $242.44   $242.45   $242.40  
  Purchase #6 $211.54   13.370%   $239.8229   $239.82   $239.80   $239.80  
  Purchase #7 $155.54   6.395%   $165.4868   $165.49   $165.50   $165.50  
  7 purchase totals = $1,163.01       $1,267.0583   $1,267.05   $1,267.00   $1,267.10