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 $242.44   13.354%   $274.8154   $274.82   $274.80   $274.80  
  Purchase #2 $241.41   9.607%   $264.6023   $264.60   $264.60   $264.60  
  Purchase #3 $217.89   12.456%   $245.0304   $245.03   $245.05   $245.00  
  Purchase #4 $11.98   13.488%   $13.5959   $13.60   $13.60   $13.60  
  Purchase #5 $61.44   4.393%   $64.1391   $64.14   $64.15   $64.10  
  Purchase #6 $72.62   3.694%   $75.3026   $75.30   $75.30   $75.30  
  Purchase #7 $102.46   10.427%   $113.1435   $113.14   $113.15   $113.10  
  7 purchase totals = $950.24       $1,050.6292   $1,050.63   $1,050.65   $1,050.50