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 $240.60   11.257%   $267.6843   $267.68   $267.70   $267.70  
  Purchase #2 $169.41   8.848%   $184.3994   $184.40   $184.40   $184.40  
  Purchase #3 $64.28   3.536%   $66.5529   $66.55   $66.55   $66.60  
  Purchase #4 $124.96   3.480%   $129.3086   $129.31   $129.30   $129.30  
  Purchase #5 $51.50   8.811%   $56.0377   $56.04   $56.05   $56.00  
  Purchase #6 $230.99   6.223%   $245.3645   $245.36   $245.35   $245.40  
  Purchase #7 $89.36   10.589%   $98.8223   $98.82   $98.80   $98.80  
  7 purchase totals = $971.10       $1,048.1697   $1,048.16   $1,048.15   $1,048.20