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 $187.31   5.317%   $197.2693   $197.27   $197.25   $197.30  
  Purchase #2 $192.76   12.202%   $216.2806   $216.28   $216.30   $216.30  
  Purchase #3 $87.70   11.862%   $98.103   $98.10   $98.10   $98.10  
  Purchase #4 $239.74   10.777%   $265.5768   $265.58   $265.60   $265.60  
  Purchase #5 $108.61   13.835%   $123.6362   $123.64   $123.65   $123.60  
  Purchase #6 $147.98   10.767%   $163.913   $163.91   $163.90   $163.90  
  Purchase #7 $204.39   3.807%   $212.1711   $212.17   $212.15   $212.20  
  7 purchase totals = $1,168.49       $1,276.9500   $1,276.95   $1,276.95   $1,277.00