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 $180.59   13.232%   $204.4857   $204.49   $204.50   $204.50  
  Purchase #2 $194.27   13.162%   $219.8398   $219.84   $219.85   $219.80  
  Purchase #3 $48.48   3.242%   $50.0517   $50.05   $50.05   $50.10  
  Purchase #4 $125.73   5.119%   $132.1661   $132.17   $132.15   $132.20  
  Purchase #5 $8.50   9.482%   $9.306   $9.31   $9.30   $9.30  
  Purchase #6 $182.64   3.259%   $188.5922   $188.59   $188.60   $188.60  
  Purchase #7 $214.51   12.578%   $241.4911   $241.49   $241.50   $241.50  
  7 purchase totals = $954.72       $1,045.9326   $1,045.94   $1,045.95   $1,046.00