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 $226.85   9.581%   $248.5845   $248.58   $248.60   $248.60  
  Purchase #2 $60.44   9.246%   $66.0283   $66.03   $66.05   $66.00  
  Purchase #3 $141.38   7.565%   $152.0754   $152.08   $152.10   $152.10  
  Purchase #4 $51.57   12.217%   $57.8703   $57.87   $57.85   $57.90  
  Purchase #5 $12.87   4.257%   $13.4179   $13.42   $13.40   $13.40  
  Purchase #6 $95.94   7.316%   $102.959   $102.96   $102.95   $103.00  
  Purchase #7 $55.54   8.651%   $60.3448   $60.34   $60.35   $60.30  
  7 purchase totals = $644.59       $701.2802   $701.28   $701.30   $701.30