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 $239.48   11.475%   $266.9603   $266.96   $266.95   $267.00  
  Purchase #2 $32.49   6.302%   $34.5375   $34.54   $34.55   $34.50  
  Purchase #3 $87.29   12.300%   $98.0267   $98.03   $98.05   $98.00  
  Purchase #4 $111.58   5.454%   $117.6656   $117.67   $117.65   $117.70  
  Purchase #5 $8.94   12.213%   $10.0318   $10.03   $10.05   $10.00  
  Purchase #6 $234.78   4.595%   $245.5681   $245.57   $245.55   $245.60  
  Purchase #7 $197.49   6.662%   $210.6468   $210.65   $210.65   $210.60  
  7 purchase totals = $912.05       $983.4368   $983.45   $983.45   $983.40