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 $239.91   12.173%   $269.1142   $269.11   $269.10   $269.10  
  Purchase #2 $59.42   10.625%   $65.7334   $65.73   $65.75   $65.70  
  Purchase #3 $169.35   11.577%   $188.9556   $188.96   $188.95   $189.00  
  Purchase #4 $138.87   13.686%   $157.8757   $157.88   $157.90   $157.90  
  Purchase #5 $198.42   11.358%   $220.9565   $220.96   $220.95   $221.00  
  Purchase #6 $116.57   4.286%   $121.5662   $121.57   $121.55   $121.60  
  Purchase #7 $140.41   8.280%   $152.0359   $152.04   $152.05   $152.00  
  7 purchase totals = $1,062.95       $1,176.2375   $1,176.25   $1,176.25   $1,176.30