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 $81.71   3.151%   $84.2847   $84.28   $84.30   $84.30  
  Purchase #2 $50.60   10.276%   $55.7997   $55.80   $55.80   $55.80  
  Purchase #3 $73.50   8.387%   $79.6644   $79.66   $79.65   $79.70  
  Purchase #4 $65.63   12.447%   $73.799   $73.80   $73.80   $73.80  
  Purchase #5 $130.44   3.712%   $135.2819   $135.28   $135.30   $135.30  
  Purchase #6 $216.52   13.436%   $245.6116   $245.61   $245.60   $245.60  
  Purchase #7 $206.52   5.735%   $218.3639   $218.36   $218.35   $218.40  
  7 purchase totals = $824.92       $892.8052   $892.79   $892.80   $892.90