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 $33.44   6.216%   $35.5186   $35.52   $35.50   $35.50  
  Purchase #2 $193.91   7.648%   $208.7402   $208.74   $208.75   $208.70  
  Purchase #3 $192.66   5.633%   $203.5125   $203.51   $203.50   $203.50  
  Purchase #4 $177.84   4.779%   $186.339   $186.34   $186.35   $186.30  
  Purchase #5 $87.35   11.356%   $97.2695   $97.27   $97.25   $97.30  
  Purchase #6 $146.44   10.448%   $161.7401   $161.74   $161.75   $161.70  
  Purchase #7 $165.96   9.801%   $182.2257   $182.23   $182.25   $182.20  
  7 purchase totals = $997.60       $1,075.3456   $1,075.35   $1,075.35   $1,075.20