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 $66.57   8.554%   $72.2644   $72.26   $72.25   $72.30  
  Purchase #2 $121.40   11.741%   $135.6536   $135.65   $135.65   $135.70  
  Purchase #3 $168.87   10.771%   $187.059   $187.06   $187.05   $187.10  
  Purchase #4 $76.29   12.173%   $85.5768   $85.58   $85.60   $85.60  
  Purchase #5 $9.27   7.433%   $9.959   $9.96   $9.95   $10.00  
  Purchase #6 $69.73   12.329%   $78.327   $78.33   $78.35   $78.30  
  Purchase #7 $199.86   11.352%   $222.5481   $222.55   $222.55   $222.50  
  7 purchase totals = $711.99       $791.3879   $791.39   $791.40   $791.50