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 $68.56   10.824%   $75.9809   $75.98   $76.00   $76.00  
  Purchase #2 $168.89   4.786%   $176.9731   $176.97   $176.95   $177.00  
  Purchase #3 $44.87   10.322%   $49.5015   $49.50   $49.50   $49.50  
  Purchase #4 $13.54   4.154%   $14.1025   $14.10   $14.10   $14.10  
  Purchase #5 $236.62   6.411%   $251.7897   $251.79   $251.80   $251.80  
  Purchase #6 $240.44   11.274%   $267.5472   $267.55   $267.55   $267.50  
  Purchase #7 $231.63   5.547%   $244.4785   $244.48   $244.50   $244.50  
  7 purchase totals = $1,004.55       $1,080.3734   $1,080.37   $1,080.40   $1,080.40