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 $68.57   8.119%   $74.1372   $74.14   $74.15   $74.10  
  Purchase #2 $32.92   7.439%   $35.3689   $35.37   $35.35   $35.40  
  Purchase #3 $81.50   12.626%   $91.7902   $91.79   $91.80   $91.80  
  Purchase #4 $224.36   4.327%   $234.0681   $234.07   $234.05   $234.10  
  Purchase #5 $67.29   10.149%   $74.1193   $74.12   $74.10   $74.10  
  Purchase #6 $130.61   7.605%   $140.5429   $140.54   $140.55   $140.50  
  Purchase #7 $147.59   3.871%   $153.3032   $153.30   $153.30   $153.30  
  7 purchase totals = $752.84       $803.3298   $803.33   $803.30   $803.30