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 $181.25   5.161%   $190.6043   $190.60   $190.60   $190.60  
  Purchase #2 $245.86   11.179%   $273.3447   $273.34   $273.35   $273.30  
  Purchase #3 $233.27   10.768%   $258.3885   $258.39   $258.40   $258.40  
  Purchase #4 $40.46   4.665%   $42.3475   $42.35   $42.35   $42.30  
  Purchase #5 $77.65   8.643%   $84.3613   $84.36   $84.35   $84.40  
  Purchase #6 $12.64   13.737%   $14.3764   $14.38   $14.40   $14.40  
  Purchase #7 $103.62   5.827%   $109.6579   $109.66   $109.65   $109.70  
  7 purchase totals = $894.75       $973.0806   $973.08   $973.10   $973.10