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 $197.38   10.143%   $217.4003   $217.40   $217.40   $217.40  
  Purchase #2 $104.27   8.663%   $113.3029   $113.30   $113.30   $113.30  
  Purchase #3 $177.66   13.701%   $202.0012   $202.00   $202.00   $202.00  
  Purchase #4 $232.83   10.239%   $256.6695   $256.67   $256.65   $256.70  
  Purchase #5 $123.48   10.330%   $136.2355   $136.24   $136.25   $136.20  
  Purchase #6 $212.50   4.346%   $221.7353   $221.74   $221.75   $221.70  
  Purchase #7 $51.30   11.167%   $57.0287   $57.03   $57.05   $57.00  
  7 purchase totals = $1,099.42       $1,204.3734   $1,204.38   $1,204.40   $1,204.30