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 $23.79   11.492%   $26.5239   $26.52   $26.50   $26.50  
  Purchase #2 $96.75   9.563%   $106.0022   $106.00   $106.00   $106.00  
  Purchase #3 $125.32   7.808%   $135.105   $135.11   $135.10   $135.10  
  Purchase #4 $225.86   10.213%   $248.9271   $248.93   $248.95   $248.90  
  Purchase #5 $134.50   9.482%   $147.2533   $147.25   $147.25   $147.30  
  Purchase #6 $224.73   7.610%   $241.832   $241.83   $241.85   $241.80  
  Purchase #7 $216.41   12.644%   $243.7729   $243.77   $243.75   $243.80  
  7 purchase totals = $1,047.36       $1,149.4164   $1,149.41   $1,149.40   $1,149.40