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 $63.77   7.548%   $68.5834   $68.58   $68.60   $68.60  
  Purchase #2 $83.82   10.493%   $92.6152   $92.62   $92.60   $92.60  
  Purchase #3 $212.30   9.683%   $232.857   $232.86   $232.85   $232.90  
  Purchase #4 $138.75   6.348%   $147.5579   $147.56   $147.55   $147.60  
  Purchase #5 $209.28   3.333%   $216.2553   $216.26   $216.25   $216.30  
  Purchase #6 $223.83   4.309%   $233.4748   $233.47   $233.45   $233.50  
  Purchase #7 $113.53   11.806%   $126.9334   $126.93   $126.95   $126.90  
  7 purchase totals = $1,045.28       $1,118.2770   $1,118.28   $1,118.25   $1,118.40