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 $147.76   12.378%   $166.0497   $166.05   $166.05   $166.00  
  Purchase #2 $219.62   12.398%   $246.8485   $246.85   $246.85   $246.80  
  Purchase #3 $108.31   13.259%   $122.6708   $122.67   $122.65   $122.70  
  Purchase #4 $60.38   12.458%   $67.9021   $67.90   $67.90   $67.90  
  Purchase #5 $47.40   12.475%   $53.3132   $53.31   $53.30   $53.30  
  Purchase #6 $159.44   5.345%   $167.9621   $167.96   $167.95   $168.00  
  Purchase #7 $162.74   13.840%   $185.2632   $185.26   $185.25   $185.30  
  7 purchase totals = $905.65       $1,010.0096   $1,010.00   $1,009.95   $1,010.00