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 $96.38   13.722%   $109.6053   $109.61   $109.60   $109.60  
  Purchase #2 $208.60   4.623%   $218.2436   $218.24   $218.25   $218.20  
  Purchase #3 $242.30   3.824%   $251.5656   $251.57   $251.55   $251.60  
  Purchase #4 $107.75   5.357%   $113.5222   $113.52   $113.50   $113.50  
  Purchase #5 $115.60   12.218%   $129.724   $129.72   $129.70   $129.70  
  Purchase #6 $176.67   10.130%   $194.5667   $194.57   $194.55   $194.60  
  Purchase #7 $35.36   3.135%   $36.4685   $36.47   $36.45   $36.50  
  7 purchase totals = $982.66       $1,053.6959   $1,053.70   $1,053.60   $1,053.70