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 $208.26   7.538%   $223.9586   $223.96   $223.95   $224.00  
  Purchase #2 $15.34   8.408%   $16.6298   $16.63   $16.65   $16.60  
  Purchase #3 $187.77   4.694%   $196.5839   $196.58   $196.60   $196.60  
  Purchase #4 $213.95   5.841%   $226.4468   $226.45   $226.45   $226.40  
  Purchase #5 $159.87   9.453%   $174.9825   $174.98   $175.00   $175.00  
  Purchase #6 $177.32   13.792%   $201.776   $201.78   $201.80   $201.80  
  Purchase #7 $128.59   5.579%   $135.764   $135.76   $135.75   $135.80  
  7 purchase totals = $1,091.10       $1,176.1416   $1,176.14   $1,176.20   $1,176.20