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 $71.66   5.412%   $75.5382   $75.54   $75.55   $75.50  
  Purchase #2 $94.55   8.486%   $102.5735   $102.57   $102.55   $102.60  
  Purchase #3 $173.66   6.854%   $185.5627   $185.56   $185.55   $185.60  
  Purchase #4 $44.27   6.292%   $47.0555   $47.06   $47.05   $47.10  
  Purchase #5 $72.39   13.543%   $82.1938   $82.19   $82.20   $82.20  
  Purchase #6 $211.29   8.400%   $229.0384   $229.04   $229.05   $229.00  
  Purchase #7 $16.95   8.401%   $18.374   $18.37   $18.35   $18.40  
  7 purchase totals = $684.77       $740.3361   $740.33   $740.30   $740.40