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 $125.69   5.688%   $132.8392   $132.84   $132.85   $132.80  
  Purchase #2 $194.71   10.521%   $215.1954   $215.20   $215.20   $215.20  
  Purchase #3 $72.50   13.182%   $82.057   $82.06   $82.05   $82.10  
  Purchase #4 $27.94   3.801%   $29.002   $29.00   $29.00   $29.00  
  Purchase #5 $230.34   7.583%   $247.8067   $247.81   $247.80   $247.80  
  Purchase #6 $176.79   12.517%   $198.9188   $198.92   $198.90   $198.90  
  Purchase #7 $232.55   4.494%   $243.0008   $243.00   $243.00   $243.00  
  7 purchase totals = $1,060.52       $1,148.8199   $1,148.83   $1,148.80   $1,148.80