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 $60.88   7.829%   $65.6463   $65.65   $65.65   $65.60  
  Purchase #2 $176.27   9.443%   $192.9152   $192.92   $192.90   $192.90  
  Purchase #3 $166.33   4.818%   $174.3438   $174.34   $174.35   $174.30  
  Purchase #4 $74.38   9.278%   $81.281   $81.28   $81.30   $81.30  
  Purchase #5 $46.30   10.717%   $51.262   $51.26   $51.25   $51.30  
  Purchase #6 $147.33   13.667%   $167.4656   $167.47   $167.45   $167.50  
  Purchase #7 $13.78   11.396%   $15.3504   $15.35   $15.35   $15.40  
  7 purchase totals = $685.27       $748.2643   $748.27   $748.25   $748.30