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 $169.71   11.412%   $189.0773   $189.08   $189.10   $189.10  
  Purchase #2 $124.28   5.403%   $130.9948   $130.99   $131.00   $131.00  
  Purchase #3 $70.36   12.204%   $78.9467   $78.95   $78.95   $78.90  
  Purchase #4 $182.40   10.695%   $201.9077   $201.91   $201.90   $201.90  
  Purchase #5 $129.38   9.555%   $141.7423   $141.74   $141.75   $141.70  
  Purchase #6 $110.53   11.402%   $123.1326   $123.13   $123.15   $123.10  
  Purchase #7 $228.43   13.765%   $259.8734   $259.87   $259.85   $259.90  
  7 purchase totals = $1,015.09       $1,125.6748   $1,125.67   $1,125.70   $1,125.60