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 $86.50   10.781%   $95.8256   $95.83   $95.85   $95.80  
  Purchase #2 $12.32   11.353%   $13.7187   $13.72   $13.70   $13.70  
  Purchase #3 $114.45   10.728%   $126.7282   $126.73   $126.75   $126.70  
  Purchase #4 $202.45   6.204%   $215.01   $215.01   $215.00   $215.00  
  Purchase #5 $189.75   6.545%   $202.1691   $202.17   $202.15   $202.20  
  Purchase #6 $220.49   9.197%   $240.7685   $240.77   $240.75   $240.80  
  Purchase #7 $121.66   12.553%   $136.932   $136.93   $136.95   $136.90  
  7 purchase totals = $947.62       $1,031.1521   $1,031.16   $1,031.15   $1,031.10