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 $43.37   10.322%   $47.8467   $47.85   $47.85   $47.80  
  Purchase #2 $232.99   5.564%   $245.9536   $245.95   $245.95   $246.00  
  Purchase #3 $136.39   5.177%   $143.4509   $143.45   $143.45   $143.50  
  Purchase #4 $222.65   9.870%   $244.6256   $244.63   $244.65   $244.60  
  Purchase #5 $88.74   5.174%   $93.3314   $93.33   $93.35   $93.30  
  Purchase #6 $105.37   3.425%   $108.9789   $108.98   $109.00   $109.00  
  Purchase #7 $25.72   6.798%   $27.4684   $27.47   $27.45   $27.50  
  7 purchase totals = $855.23       $911.6555   $911.66   $911.70   $911.70