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 $68.26   8.116%   $73.8   $73.80   $73.80   $73.80  
  Purchase #2 $239.51   3.525%   $247.9527   $247.95   $247.95   $248.00  
  Purchase #3 $52.92   3.499%   $54.7717   $54.77   $54.75   $54.80  
  Purchase #4 $91.29   11.374%   $101.6733   $101.67   $101.65   $101.70  
  Purchase #5 $94.61   11.798%   $105.7721   $105.77   $105.75   $105.80  
  Purchase #6 $193.55   9.865%   $212.6437   $212.64   $212.65   $212.60  
  Purchase #7 $63.46   10.254%   $69.9672   $69.97   $69.95   $70.00  
  7 purchase totals = $803.60       $866.5807   $866.57   $866.50   $866.70