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 $234.26   12.267%   $262.9967   $263.00   $263.00   $263.00  
  Purchase #2 $140.59   10.530%   $155.3941   $155.39   $155.40   $155.40  
  Purchase #3 $35.40   12.599%   $39.86   $39.86   $39.85   $39.90  
  Purchase #4 $246.91   10.605%   $273.0948   $273.09   $273.10   $273.10  
  Purchase #5 $196.30   11.449%   $218.7744   $218.77   $218.75   $218.80  
  Purchase #6 $111.56   5.720%   $117.9412   $117.94   $117.95   $117.90  
  Purchase #7 $234.97   10.418%   $259.4492   $259.45   $259.45   $259.40  
  7 purchase totals = $1,199.99       $1,327.5104   $1,327.50   $1,327.50   $1,327.50