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 $241.46   12.499%   $271.6401   $271.64   $271.65   $271.60  
  Purchase #2 $9.63   11.763%   $10.7628   $10.76   $10.75   $10.80  
  Purchase #3 $206.78   10.256%   $227.9874   $227.99   $228.00   $228.00  
  Purchase #4 $246.77   12.118%   $276.6736   $276.67   $276.65   $276.70  
  Purchase #5 $5.49   9.693%   $6.0221   $6.02   $6.00   $6.00  
  Purchase #6 $135.83   12.660%   $153.0261   $153.03   $153.05   $153.00  
  Purchase #7 $69.82   9.408%   $76.3887   $76.39   $76.40   $76.40  
  7 purchase totals = $915.78       $1,022.5008   $1,022.50   $1,022.50   $1,022.50