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 $206.44   13.705%   $234.7326   $234.73   $234.75   $234.70  
  Purchase #2 $161.44   3.768%   $167.5231   $167.52   $167.50   $167.50  
  Purchase #3 $101.38   12.536%   $114.089   $114.09   $114.10   $114.10  
  Purchase #4 $46.29   7.863%   $49.9298   $49.93   $49.95   $49.90  
  Purchase #5 $113.52   12.364%   $127.5556   $127.56   $127.55   $127.60  
  Purchase #6 $153.94   3.408%   $159.1863   $159.19   $159.20   $159.20  
  Purchase #7 $6.54   12.157%   $7.3351   $7.34   $7.35   $7.30  
  7 purchase totals = $789.55       $860.3515   $860.36   $860.40   $860.30