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 $53.54   4.504%   $55.9514   $55.95   $55.95   $56.00  
  Purchase #2 $188.96   4.580%   $197.6144   $197.61   $197.60   $197.60  
  Purchase #3 $227.35   7.843%   $245.1811   $245.18   $245.20   $245.20  
  Purchase #4 $58.35   6.691%   $62.2542   $62.25   $62.25   $62.30  
  Purchase #5 $230.63   8.661%   $250.6049   $250.60   $250.60   $250.60  
  Purchase #6 $66.35   13.146%   $75.0724   $75.07   $75.05   $75.10  
  Purchase #7 $204.60   5.146%   $215.1287   $215.13   $215.15   $215.10  
  7 purchase totals = $1,029.78       $1,101.8071   $1,101.79   $1,101.80   $1,101.90