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 $235.91   4.772%   $247.1676   $247.17   $247.15   $247.20  
  Purchase #2 $167.43   11.390%   $186.5003   $186.50   $186.50   $186.50  
  Purchase #3 $140.32   10.665%   $155.2851   $155.29   $155.30   $155.30  
  Purchase #4 $127.58   11.249%   $141.9315   $141.93   $141.95   $141.90  
  Purchase #5 $208.39   4.199%   $217.1403   $217.14   $217.15   $217.10  
  Purchase #6 $31.80   13.628%   $36.1337   $36.13   $36.15   $36.10  
  Purchase #7 $35.74   10.506%   $39.4948   $39.49   $39.50   $39.50  
  7 purchase totals = $947.17       $1,023.6533   $1,023.65   $1,023.70   $1,023.60