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 $179.60   12.820%   $202.6247   $202.62   $202.60   $202.60  
  Purchase #2 $230.27   10.814%   $255.1714   $255.17   $255.15   $255.20  
  Purchase #3 $125.52   6.406%   $133.5608   $133.56   $133.55   $133.60  
  Purchase #4 $172.67   13.494%   $195.9701   $195.97   $195.95   $196.00  
  Purchase #5 $157.89   3.361%   $163.1967   $163.20   $163.20   $163.20  
  Purchase #6 $60.93   9.347%   $66.6251   $66.63   $66.65   $66.60  
  Purchase #7 $224.71   4.804%   $235.5051   $235.51   $235.50   $235.50  
  7 purchase totals = $1,151.59       $1,252.6539   $1,252.66   $1,252.60   $1,252.70