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 $240.38   5.662%   $253.9903   $253.99   $254.00   $254.00  
  Purchase #2 $137.65   5.781%   $145.6075   $145.61   $145.60   $145.60  
  Purchase #3 $23.26   11.124%   $25.8474   $25.85   $25.85   $25.80  
  Purchase #4 $31.82   7.133%   $34.0897   $34.09   $34.10   $34.10  
  Purchase #5 $219.44   12.727%   $247.3681   $247.37   $247.35   $247.40  
  Purchase #6 $230.69   6.831%   $246.4484   $246.45   $246.45   $246.40  
  Purchase #7 $237.52   6.478%   $252.9065   $252.91   $252.90   $252.90  
  7 purchase totals = $1,120.76       $1,206.2579   $1,206.27   $1,206.25   $1,206.20