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 $233.95   11.554%   $260.9806   $260.98   $261.00   $261.00  
  Purchase #2 $174.77   9.796%   $191.8905   $191.89   $191.90   $191.90  
  Purchase #3 $91.67   6.591%   $97.712   $97.71   $97.70   $97.70  
  Purchase #4 $72.74   13.642%   $82.6632   $82.66   $82.65   $82.70  
  Purchase #5 $188.50   13.232%   $213.4423   $213.44   $213.45   $213.40  
  Purchase #6 $243.54   12.487%   $273.9508   $273.95   $273.95   $274.00  
  Purchase #7 $6.73   12.107%   $7.5448   $7.54   $7.55   $7.50  
  7 purchase totals = $1,011.90       $1,128.1842   $1,128.17   $1,128.20   $1,128.20