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 $55.90   12.339%   $62.7975   $62.80   $62.80   $62.80  
  Purchase #2 $173.54   10.294%   $191.4042   $191.40   $191.40   $191.40  
  Purchase #3 $200.46   12.270%   $225.0564   $225.06   $225.05   $225.10  
  Purchase #4 $240.48   11.464%   $268.0486   $268.05   $268.05   $268.00  
  Purchase #5 $207.44   12.315%   $232.9862   $232.99   $233.00   $233.00  
  Purchase #6 $114.56   8.783%   $124.6218   $124.62   $124.60   $124.60  
  Purchase #7 $103.86   12.788%   $117.1416   $117.14   $117.15   $117.10  
  7 purchase totals = $1,096.24       $1,222.0563   $1,222.06   $1,222.05   $1,222.00