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 $246.90   5.383%   $260.1906   $260.19   $260.20   $260.20  
  Purchase #2 $139.93   9.664%   $153.4528   $153.45   $153.45   $153.50  
  Purchase #3 $138.77   10.613%   $153.4977   $153.50   $153.50   $153.50  
  Purchase #4 $155.67   4.715%   $163.0098   $163.01   $163.00   $163.00  
  Purchase #5 $233.98   5.270%   $246.3107   $246.31   $246.30   $246.30  
  Purchase #6 $79.86   8.759%   $86.8549   $86.85   $86.85   $86.90  
  Purchase #7 $180.54   7.313%   $193.7429   $193.74   $193.75   $193.70  
  7 purchase totals = $1,175.65       $1,257.0594   $1,257.05   $1,257.05   $1,257.10