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 $234.74   9.486%   $257.0074   $257.01   $257.00   $257.00  
  Purchase #2 $160.61   13.632%   $182.5044   $182.50   $182.50   $182.50  
  Purchase #3 $51.69   4.321%   $53.9235   $53.92   $53.90   $53.90  
  Purchase #4 $138.26   3.619%   $143.2636   $143.26   $143.25   $143.30  
  Purchase #5 $198.87   4.132%   $207.0873   $207.09   $207.10   $207.10  
  Purchase #6 $246.26   8.821%   $267.9826   $267.98   $268.00   $268.00  
  Purchase #7 $223.40   7.562%   $240.2935   $240.29   $240.30   $240.30  
  7 purchase totals = $1,253.83       $1,352.0623   $1,352.05   $1,352.05   $1,352.10