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 $182.27   13.327%   $206.5611   $206.56   $206.55   $206.60  
  Purchase #2 $162.53   7.263%   $174.3346   $174.33   $174.35   $174.30  
  Purchase #3 $57.35   12.681%   $64.6226   $64.62   $64.60   $64.60  
  Purchase #4 $158.64   5.627%   $167.5667   $167.57   $167.55   $167.60  
  Purchase #5 $44.77   3.354%   $46.2716   $46.27   $46.25   $46.30  
  Purchase #6 $34.94   11.774%   $39.0538   $39.05   $39.05   $39.10  
  Purchase #7 $61.57   7.675%   $66.2955   $66.30   $66.30   $66.30  
  7 purchase totals = $702.07       $764.7059   $764.70   $764.65   $764.80