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 $196.79   13.532%   $223.4196   $223.42   $223.40   $223.40  
  Purchase #2 $142.61   9.316%   $155.8955   $155.90   $155.90   $155.90  
  Purchase #3 $192.32   12.491%   $216.3427   $216.34   $216.35   $216.30  
  Purchase #4 $174.47   4.596%   $182.4886   $182.49   $182.50   $182.50  
  Purchase #5 $52.64   5.697%   $55.6389   $55.64   $55.65   $55.60  
  Purchase #6 $184.65   12.217%   $207.2087   $207.21   $207.20   $207.20  
  Purchase #7 $124.32   11.365%   $138.449   $138.45   $138.45   $138.40  
  7 purchase totals = $1,067.80       $1,179.4430   $1,179.45   $1,179.45   $1,179.30