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 $114.94   11.605%   $128.2788   $128.28   $128.30   $128.30  
  Purchase #2 $145.83   6.329%   $155.0596   $155.06   $155.05   $155.10  
  Purchase #3 $44.88   11.545%   $50.0614   $50.06   $50.05   $50.10  
  Purchase #4 $208.29   3.326%   $215.2177   $215.22   $215.20   $215.20  
  Purchase #5 $141.27   12.752%   $159.2848   $159.28   $159.30   $159.30  
  Purchase #6 $210.85   4.773%   $220.9139   $220.91   $220.90   $220.90  
  Purchase #7 $88.98   9.767%   $97.6707   $97.67   $97.65   $97.70  
  7 purchase totals = $955.04       $1,026.4869   $1,026.48   $1,026.45   $1,026.60