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 $56.46   7.436%   $60.6584   $60.66   $60.65   $60.70  
  Purchase #2 $188.78   10.865%   $209.2909   $209.29   $209.30   $209.30  
  Purchase #3 $86.55   5.237%   $91.0826   $91.08   $91.10   $91.10  
  Purchase #4 $106.37   4.728%   $111.3992   $111.40   $111.40   $111.40  
  Purchase #5 $201.94   11.838%   $225.8457   $225.85   $225.85   $225.80  
  Purchase #6 $192.36   8.219%   $208.1701   $208.17   $208.15   $208.20  
  Purchase #7 $108.77   5.586%   $114.8459   $114.85   $114.85   $114.80  
  7 purchase totals = $941.23       $1,021.2928   $1,021.30   $1,021.30   $1,021.30