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 $242.36   7.660%   $260.9248   $260.92   $260.90   $260.90  
  Purchase #2 $142.89   6.200%   $151.7492   $151.75   $151.75   $151.70  
  Purchase #3 $19.61   4.717%   $20.535   $20.54   $20.55   $20.50  
  Purchase #4 $194.97   12.510%   $219.3607   $219.36   $219.35   $219.40  
  Purchase #5 $183.67   8.424%   $199.1424   $199.14   $199.15   $199.10  
  Purchase #6 $141.46   12.712%   $159.4424   $159.44   $159.45   $159.40  
  Purchase #7 $236.57   8.207%   $255.9853   $255.99   $256.00   $256.00  
  7 purchase totals = $1,161.53       $1,267.1398   $1,267.14   $1,267.15   $1,267.00