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 $103.86   5.197%   $109.2576   $109.26   $109.25   $109.30  
  Purchase #2 $218.96   11.111%   $243.2886   $243.29   $243.30   $243.30  
  Purchase #3 $138.77   13.565%   $157.5942   $157.59   $157.60   $157.60  
  Purchase #4 $114.73   4.778%   $120.2118   $120.21   $120.20   $120.20  
  Purchase #5 $75.34   12.157%   $84.4991   $84.50   $84.50   $84.50  
  Purchase #6 $219.25   11.200%   $243.806   $243.81   $243.80   $243.80  
  Purchase #7 $191.92   8.607%   $208.4386   $208.44   $208.45   $208.40  
  7 purchase totals = $1,062.83       $1,167.0959   $1,167.10   $1,167.10   $1,167.10