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 $44.30   6.569%   $47.2101   $47.21   $47.20   $47.20  
  Purchase #2 $244.45   13.704%   $277.9494   $277.95   $277.95   $277.90  
  Purchase #3 $148.90   5.816%   $157.56   $157.56   $157.55   $157.60  
  Purchase #4 $175.99   13.760%   $200.2062   $200.21   $200.20   $200.20  
  Purchase #5 $140.90   10.764%   $156.0665   $156.07   $156.05   $156.10  
  Purchase #6 $110.63   5.303%   $116.4967   $116.50   $116.50   $116.50  
  Purchase #7 $116.81   5.693%   $123.46   $123.46   $123.45   $123.50  
  7 purchase totals = $981.98       $1,078.9489   $1,078.96   $1,078.90   $1,079.00