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 $53.94   3.694%   $55.9325   $55.93   $55.95   $55.90  
  Purchase #2 $181.27   13.686%   $206.0786   $206.08   $206.10   $206.10  
  Purchase #3 $106.76   5.159%   $112.2677   $112.27   $112.25   $112.30  
  Purchase #4 $248.75   7.385%   $267.1202   $267.12   $267.10   $267.10  
  Purchase #5 $44.32   4.319%   $46.2342   $46.23   $46.25   $46.20  
  Purchase #6 $226.39   13.768%   $257.5594   $257.56   $257.55   $257.60  
  Purchase #7 $209.51   5.615%   $221.274   $221.27   $221.25   $221.30  
  7 purchase totals = $1,070.94       $1,166.4666   $1,166.46   $1,166.45   $1,166.50