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 $239.84   7.236%   $257.1948   $257.19   $257.20   $257.20  
  Purchase #2 $68.66   10.161%   $75.6365   $75.64   $75.65   $75.60  
  Purchase #3 $111.33   5.709%   $117.6858   $117.69   $117.70   $117.70  
  Purchase #4 $183.43   6.156%   $194.722   $194.72   $194.70   $194.70  
  Purchase #5 $77.71   12.647%   $87.538   $87.54   $87.55   $87.50  
  Purchase #6 $217.94   6.413%   $231.9165   $231.92   $231.90   $231.90  
  Purchase #7 $84.63   4.697%   $88.6051   $88.61   $88.60   $88.60  
  7 purchase totals = $983.54       $1,053.2987   $1,053.31   $1,053.30   $1,053.20