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 $83.77   5.865%   $88.6831   $88.68   $88.70   $88.70  
  Purchase #2 $44.26   8.356%   $47.9584   $47.96   $47.95   $48.00  
  Purchase #3 $229.86   11.839%   $257.0731   $257.07   $257.05   $257.10  
  Purchase #4 $179.96   13.652%   $204.5281   $204.53   $204.55   $204.50  
  Purchase #5 $102.38   10.745%   $113.3807   $113.38   $113.40   $113.40  
  Purchase #6 $60.77   4.505%   $63.5077   $63.51   $63.50   $63.50  
  Purchase #7 $205.61   12.802%   $231.9322   $231.93   $231.95   $231.90  
  7 purchase totals = $906.61       $1,007.0633   $1,007.06   $1,007.10   $1,007.10