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 $241.83   10.714%   $267.7397   $267.74   $267.75   $267.70  
  Purchase #2 $5.72   12.168%   $6.416   $6.42   $6.40   $6.40  
  Purchase #3 $55.51   11.825%   $62.0741   $62.07   $62.05   $62.10  
  Purchase #4 $23.58   8.195%   $25.5124   $25.51   $25.50   $25.50  
  Purchase #5 $246.95   6.499%   $262.9993   $263.00   $263.00   $263.00  
  Purchase #6 $26.54   12.682%   $29.9058   $29.91   $29.90   $29.90  
  Purchase #7 $176.99   13.773%   $201.3668   $201.37   $201.35   $201.40  
  7 purchase totals = $777.12       $856.0141   $856.02   $855.95   $856.00