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 $44.32   5.597%   $46.8006   $46.80   $46.80   $46.80  
  Purchase #2 $111.59   8.726%   $121.3273   $121.33   $121.35   $121.30  
  Purchase #3 $221.88   10.850%   $245.954   $245.95   $245.95   $246.00  
  Purchase #4 $93.47   8.344%   $101.2691   $101.27   $101.25   $101.30  
  Purchase #5 $57.86   5.442%   $61.0087   $61.01   $61.00   $61.00  
  Purchase #6 $146.54   13.805%   $166.7698   $166.77   $166.75   $166.80  
  Purchase #7 $231.60   13.625%   $263.1555   $263.16   $263.15   $263.20  
  7 purchase totals = $907.26       $1,006.2850   $1,006.29   $1,006.25   $1,006.40