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 $95.89   9.233%   $104.7435   $104.74   $104.75   $104.70  
  Purchase #2 $142.82   9.413%   $156.2636   $156.26   $156.25   $156.30  
  Purchase #3 $190.59   12.820%   $215.0236   $215.02   $215.00   $215.00  
  Purchase #4 $206.43   12.654%   $232.5517   $232.55   $232.55   $232.60  
  Purchase #5 $118.90   9.785%   $130.5344   $130.53   $130.55   $130.50  
  Purchase #6 $202.25   6.262%   $214.9149   $214.91   $214.90   $214.90  
  Purchase #7 $125.45   5.631%   $132.5141   $132.51   $132.50   $132.50  
  7 purchase totals = $1,082.33       $1,186.5458   $1,186.52   $1,186.50   $1,186.50