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 $120.65   11.517%   $134.5453   $134.55   $134.55   $134.50  
  Purchase #2 $65.28   4.573%   $68.2653   $68.27   $68.25   $68.30  
  Purchase #3 $155.62   7.821%   $167.791   $167.79   $167.80   $167.80  
  Purchase #4 $136.95   8.854%   $149.0756   $149.08   $149.10   $149.10  
  Purchase #5 $244.83   4.293%   $255.3406   $255.34   $255.35   $255.30  
  Purchase #6 $113.76   3.272%   $117.4822   $117.48   $117.50   $117.50  
  Purchase #7 $157.34   11.244%   $175.0313   $175.03   $175.05   $175.00  
  7 purchase totals = $994.43       $1,067.5313   $1,067.54   $1,067.60   $1,067.50