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 $39.36   11.769%   $43.9923   $43.99   $44.00   $44.00  
  Purchase #2 $214.32   10.556%   $236.9436   $236.94   $236.95   $236.90  
  Purchase #3 $56.32   6.355%   $59.8991   $59.90   $59.90   $59.90  
  Purchase #4 $121.83   12.596%   $137.1757   $137.18   $137.20   $137.20  
  Purchase #5 $144.51   12.704%   $162.8686   $162.87   $162.85   $162.90  
  Purchase #6 $149.44   11.854%   $167.1546   $167.15   $167.15   $167.20  
  Purchase #7 $153.52   5.463%   $161.9068   $161.91   $161.90   $161.90  
  7 purchase totals = $879.30       $969.9407   $969.94   $969.95   $970.00