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 $199.52   13.382%   $226.2198   $226.22   $226.20   $226.20  
  Purchase #2 $46.35   6.682%   $49.4471   $49.45   $49.45   $49.40  
  Purchase #3 $50.82   6.278%   $54.0105   $54.01   $54.00   $54.00  
  Purchase #4 $132.66   5.728%   $140.2588   $140.26   $140.25   $140.30  
  Purchase #5 $174.48   12.328%   $195.9899   $195.99   $196.00   $196.00  
  Purchase #6 $158.96   12.607%   $179.0001   $179.00   $179.00   $179.00  
  Purchase #7 $85.96   12.420%   $96.6362   $96.64   $96.65   $96.60  
  7 purchase totals = $848.75       $941.5624   $941.57   $941.55   $941.50