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 $82.85   6.282%   $88.0546   $88.05   $88.05   $88.10  
  Purchase #2 $179.54   11.366%   $199.9465   $199.95   $199.95   $199.90  
  Purchase #3 $167.34   9.857%   $183.8347   $183.83   $183.85   $183.80  
  Purchase #4 $63.26   5.426%   $66.6925   $66.69   $66.70   $66.70  
  Purchase #5 $47.75   9.222%   $52.1535   $52.15   $52.15   $52.20  
  Purchase #6 $231.32   4.276%   $241.2112   $241.21   $241.20   $241.20  
  Purchase #7 $168.71   3.569%   $174.7313   $174.73   $174.75   $174.70  
  7 purchase totals = $940.77       $1,006.6243   $1,006.61   $1,006.65   $1,006.60