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 $239.94   10.259%   $264.5554   $264.56   $264.55   $264.60  
  Purchase #2 $26.38   4.392%   $27.5386   $27.54   $27.55   $27.50  
  Purchase #3 $236.86   4.594%   $247.7413   $247.74   $247.75   $247.70  
  Purchase #4 $206.35   12.447%   $232.0344   $232.03   $232.05   $232.00  
  Purchase #5 $107.68   13.329%   $122.0327   $122.03   $122.05   $122.00  
  Purchase #6 $241.88   4.378%   $252.4695   $252.47   $252.45   $252.50  
  Purchase #7 $93.50   3.406%   $96.6846   $96.68   $96.70   $96.70  
  7 purchase totals = $1,152.59       $1,243.0565   $1,243.05   $1,243.10   $1,243.00