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 $208.84   4.702%   $218.6597   $218.66   $218.65   $218.70  
  Purchase #2 $154.54   8.119%   $167.0871   $167.09   $167.10   $167.10  
  Purchase #3 $233.39   9.265%   $255.0136   $255.01   $255.00   $255.00  
  Purchase #4 $55.29   9.791%   $60.7034   $60.70   $60.70   $60.70  
  Purchase #5 $80.90   4.796%   $84.78   $84.78   $84.80   $84.80  
  Purchase #6 $87.48   8.698%   $95.089   $95.09   $95.10   $95.10  
  Purchase #7 $78.39   7.605%   $84.3516   $84.35   $84.35   $84.40  
  7 purchase totals = $898.83       $965.6844   $965.68   $965.70   $965.80