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 $86.63   13.525%   $98.3467   $98.35   $98.35   $98.30  
  Purchase #2 $109.40   12.732%   $123.3288   $123.33   $123.35   $123.30  
  Purchase #3 $66.36   3.745%   $68.8452   $68.85   $68.85   $68.80  
  Purchase #4 $213.53   11.596%   $238.2909   $238.29   $238.30   $238.30  
  Purchase #5 $30.38   10.376%   $33.5322   $33.53   $33.55   $33.50  
  Purchase #6 $167.39   9.552%   $183.3791   $183.38   $183.40   $183.40  
  Purchase #7 $98.91   9.440%   $108.2471   $108.25   $108.25   $108.20  
  7 purchase totals = $772.60       $853.9700   $853.98   $854.05   $853.80