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 $69.62   12.725%   $78.4791   $78.48   $78.50   $78.50  
  Purchase #2 $154.61   11.387%   $172.2154   $172.22   $172.20   $172.20  
  Purchase #3 $180.99   11.508%   $201.8183   $201.82   $201.80   $201.80  
  Purchase #4 $118.55   7.644%   $127.612   $127.61   $127.60   $127.60  
  Purchase #5 $229.75   5.725%   $242.9032   $242.90   $242.90   $242.90  
  Purchase #6 $69.74   8.312%   $75.5368   $75.54   $75.55   $75.50  
  Purchase #7 $246.26   4.811%   $258.1076   $258.11   $258.10   $258.10  
  7 purchase totals = $1,069.52       $1,156.6724   $1,156.68   $1,156.65   $1,156.60