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 $177.43   8.124%   $191.8444   $191.84   $191.85   $191.80  
  Purchase #2 $137.27   3.178%   $141.6324   $141.63   $141.65   $141.60  
  Purchase #3 $210.86   13.446%   $239.2122   $239.21   $239.20   $239.20  
  Purchase #4 $232.38   5.349%   $244.81   $244.81   $244.80   $244.80  
  Purchase #5 $88.62   3.743%   $91.937   $91.94   $91.95   $91.90  
  Purchase #6 $247.76   7.737%   $266.9292   $266.93   $266.95   $266.90  
  Purchase #7 $22.54   13.684%   $25.6244   $25.62   $25.60   $25.60  
  7 purchase totals = $1,116.86       $1,201.9896   $1,201.98   $1,202.00   $1,201.80