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 $98.45   12.763%   $111.0152   $111.02   $111.00   $111.00  
  Purchase #2 $142.68   6.278%   $151.6375   $151.64   $151.65   $151.60  
  Purchase #3 $49.60   13.415%   $56.2538   $56.25   $56.25   $56.30  
  Purchase #4 $47.69   4.197%   $49.6915   $49.69   $49.70   $49.70  
  Purchase #5 $226.53   7.470%   $243.4518   $243.45   $243.45   $243.50  
  Purchase #6 $198.61   3.742%   $206.042   $206.04   $206.05   $206.00  
  Purchase #7 $250.54   7.352%   $268.9597   $268.96   $268.95   $269.00  
  7 purchase totals = $1,014.10       $1,087.0515   $1,087.05   $1,087.05   $1,087.10