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 $61.99   12.338%   $69.6383   $69.64   $69.65   $69.60  
  Purchase #2 $234.83   13.513%   $266.5626   $266.56   $266.55   $266.60  
  Purchase #3 $61.93   9.699%   $67.9366   $67.94   $67.95   $67.90  
  Purchase #4 $200.64   6.334%   $213.3485   $213.35   $213.35   $213.30  
  Purchase #5 $157.30   6.456%   $167.4553   $167.46   $167.45   $167.50  
  Purchase #6 $136.31   9.314%   $149.0059   $149.01   $149.00   $149.00  
  Purchase #7 $24.69   8.127%   $26.6966   $26.70   $26.70   $26.70  
  7 purchase totals = $877.69       $960.6438   $960.66   $960.65   $960.60