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 $76.68   11.206%   $85.2728   $85.27   $85.25   $85.30  
  Purchase #2 $111.68   13.130%   $126.3436   $126.34   $126.35   $126.30  
  Purchase #3 $139.29   3.604%   $144.31   $144.31   $144.30   $144.30  
  Purchase #4 $155.98   6.520%   $166.1499   $166.15   $166.15   $166.10  
  Purchase #5 $224.79   5.559%   $237.2861   $237.29   $237.30   $237.30  
  Purchase #6 $30.98   10.429%   $34.2109   $34.21   $34.20   $34.20  
  Purchase #7 $211.46   4.566%   $221.1153   $221.12   $221.10   $221.10  
  7 purchase totals = $950.86       $1,014.6886   $1,014.69   $1,014.65   $1,014.60