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 $81.90   5.466%   $86.3767   $86.38   $86.40   $86.40  
  Purchase #2 $36.65   7.272%   $39.3152   $39.32   $39.30   $39.30  
  Purchase #3 $238.45   13.726%   $271.1796   $271.18   $271.20   $271.20  
  Purchase #4 $204.37   6.479%   $217.6111   $217.61   $217.60   $217.60  
  Purchase #5 $134.44   5.341%   $141.6204   $141.62   $141.60   $141.60  
  Purchase #6 $140.32   6.592%   $149.5699   $149.57   $149.55   $149.60  
  Purchase #7 $36.54   6.447%   $38.8957   $38.90   $38.90   $38.90  
  7 purchase totals = $872.67       $944.5686   $944.58   $944.55   $944.60