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 $105.65   8.458%   $114.5859   $114.59   $114.60   $114.60  
  Purchase #2 $126.71   10.570%   $140.1032   $140.10   $140.10   $140.10  
  Purchase #3 $20.44   5.764%   $21.6182   $21.62   $21.60   $21.60  
  Purchase #4 $238.57   8.679%   $259.2755   $259.28   $259.30   $259.30  
  Purchase #5 $230.85   8.482%   $250.4307   $250.43   $250.45   $250.40  
  Purchase #6 $5.71   10.840%   $6.329   $6.33   $6.35   $6.30  
  Purchase #7 $58.30   5.182%   $61.3211   $61.32   $61.30   $61.30  
  7 purchase totals = $786.23       $853.6636   $853.67   $853.70   $853.60