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 $14.28   9.148%   $15.5863   $15.59   $15.60   $15.60  
  Purchase #2 $56.49   11.464%   $62.966   $62.97   $62.95   $63.00  
  Purchase #3 $166.31   3.628%   $172.3437   $172.34   $172.35   $172.30  
  Purchase #4 $235.60   5.635%   $248.8761   $248.88   $248.90   $248.90  
  Purchase #5 $221.47   5.659%   $234.003   $234.00   $234.00   $234.00  
  Purchase #6 $154.76   4.193%   $161.2491   $161.25   $161.25   $161.20  
  Purchase #7 $184.55   7.164%   $197.7712   $197.77   $197.75   $197.80  
  7 purchase totals = $1,033.46       $1,092.7954   $1,092.80   $1,092.80   $1,092.80