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 $241.33   11.822%   $269.86   $269.86   $269.85   $269.90  
  Purchase #2 $89.35   13.589%   $101.4918   $101.49   $101.50   $101.50  
  Purchase #3 $107.75   7.717%   $116.0651   $116.07   $116.05   $116.10  
  Purchase #4 $86.89   6.721%   $92.7299   $92.73   $92.75   $92.70  
  Purchase #5 $83.70   12.826%   $94.4354   $94.44   $94.45   $94.40  
  Purchase #6 $210.68   4.769%   $220.7273   $220.73   $220.75   $220.70  
  Purchase #7 $165.46   9.188%   $180.6625   $180.66   $180.65   $180.70  
  7 purchase totals = $985.16       $1,075.9720   $1,075.98   $1,076.00   $1,076.00