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 $52.86   6.804%   $56.4566   $56.46   $56.45   $56.50  
  Purchase #2 $114.71   8.145%   $124.0531   $124.05   $124.05   $124.10  
  Purchase #3 $18.27   9.757%   $20.0526   $20.05   $20.05   $20.10  
  Purchase #4 $113.48   3.445%   $117.3894   $117.39   $117.40   $117.40  
  Purchase #5 $44.58   4.591%   $46.6267   $46.63   $46.65   $46.60  
  Purchase #6 $167.54   7.181%   $179.571   $179.57   $179.55   $179.60  
  Purchase #7 $241.67   10.485%   $267.0091   $267.01   $267.00   $267.00  
  7 purchase totals = $753.11       $811.1585   $811.16   $811.15   $811.30