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 $74.35   5.491%   $78.4326   $78.43   $78.45   $78.40  
  Purchase #2 $93.93   8.146%   $101.5815   $101.58   $101.60   $101.60  
  Purchase #3 $102.64   13.309%   $116.3004   $116.30   $116.30   $116.30  
  Purchase #4 $224.80   9.697%   $246.5989   $246.60   $246.60   $246.60  
  Purchase #5 $250.87   13.523%   $284.7952   $284.80   $284.80   $284.80  
  Purchase #6 $137.82   4.368%   $143.84   $143.84   $143.85   $143.80  
  Purchase #7 $234.59   3.485%   $242.7655   $242.77   $242.75   $242.80  
  7 purchase totals = $1,119.00       $1,214.3141   $1,214.32   $1,214.35   $1,214.30