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 $206.52   13.440%   $234.2763   $234.28   $234.30   $234.30  
  Purchase #2 $184.59   12.861%   $208.3301   $208.33   $208.35   $208.30  
  Purchase #3 $38.59   10.605%   $42.6825   $42.68   $42.70   $42.70  
  Purchase #4 $25.67   3.452%   $26.5561   $26.56   $26.55   $26.60  
  Purchase #5 $199.79   7.380%   $214.5345   $214.53   $214.55   $214.50  
  Purchase #6 $26.40   5.805%   $27.9325   $27.93   $27.95   $27.90  
  Purchase #7 $109.88   5.472%   $115.8926   $115.89   $115.90   $115.90  
  7 purchase totals = $791.44       $870.2046   $870.20   $870.30   $870.20