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 $95.72   6.569%   $102.0078   $102.01   $102.00   $102.00  
  Purchase #2 $182.38   5.308%   $192.0607   $192.06   $192.05   $192.10  
  Purchase #3 $160.68   8.298%   $174.0132   $174.01   $174.00   $174.00  
  Purchase #4 $113.74   7.688%   $122.4843   $122.48   $122.50   $122.50  
  Purchase #5 $244.33   7.233%   $262.0024   $262.00   $262.00   $262.00  
  Purchase #6 $195.34   6.534%   $208.1035   $208.10   $208.10   $208.10  
  Purchase #7 $150.45   7.717%   $162.0602   $162.06   $162.05   $162.10  
  7 purchase totals = $1,142.64       $1,222.7321   $1,222.72   $1,222.70   $1,222.80