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 $183.54   6.793%   $196.0079   $196.01   $196.00   $196.00  
  Purchase #2 $38.48   10.704%   $42.5989   $42.60   $42.60   $42.60  
  Purchase #3 $116.85   6.438%   $124.3728   $124.37   $124.35   $124.40  
  Purchase #4 $238.97   7.681%   $257.3253   $257.33   $257.35   $257.30  
  Purchase #5 $128.65   6.206%   $136.634   $136.63   $136.65   $136.60  
  Purchase #6 $153.69   4.730%   $160.9595   $160.96   $160.95   $161.00  
  Purchase #7 $98.68   6.352%   $104.9482   $104.95   $104.95   $104.90  
  7 purchase totals = $958.86       $1,022.8466   $1,022.85   $1,022.85   $1,022.80