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 $241.76   8.492%   $262.2903   $262.29   $262.30   $262.30  
  Purchase #2 $80.71   4.312%   $84.1902   $84.19   $84.20   $84.20  
  Purchase #3 $178.81   8.429%   $193.8819   $193.88   $193.90   $193.90  
  Purchase #4 $43.39   10.249%   $47.837   $47.84   $47.85   $47.80  
  Purchase #5 $159.61   3.515%   $165.2203   $165.22   $165.20   $165.20  
  Purchase #6 $63.98   4.684%   $66.9768   $66.98   $67.00   $67.00  
  Purchase #7 $228.70   4.794%   $239.6639   $239.66   $239.65   $239.70  
  7 purchase totals = $996.96       $1,060.0604   $1,060.06   $1,060.10   $1,060.10