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 $64.35   8.452%   $69.7889   $69.79   $69.80   $69.80  
  Purchase #2 $153.34   5.737%   $162.1371   $162.14   $162.15   $162.10  
  Purchase #3 $189.28   4.254%   $197.332   $197.33   $197.35   $197.30  
  Purchase #4 $9.46   9.491%   $10.3578   $10.36   $10.35   $10.40  
  Purchase #5 $59.38   4.859%   $62.2653   $62.27   $62.25   $62.30  
  Purchase #6 $201.87   3.487%   $208.9092   $208.91   $208.90   $208.90  
  Purchase #7 $224.44   7.568%   $241.4256   $241.43   $241.45   $241.40  
  7 purchase totals = $902.12       $952.2159   $952.23   $952.25   $952.20