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 $44.72   10.234%   $49.2966   $49.30   $49.30   $49.30  
  Purchase #2 $95.81   13.213%   $108.4694   $108.47   $108.45   $108.50  
  Purchase #3 $32.72   7.526%   $35.1825   $35.18   $35.20   $35.20  
  Purchase #4 $237.38   11.408%   $264.4603   $264.46   $264.45   $264.50  
  Purchase #5 $52.47   8.458%   $56.9079   $56.91   $56.90   $56.90  
  Purchase #6 $188.91   6.294%   $200.8   $200.80   $200.80   $200.80  
  Purchase #7 $147.39   4.832%   $154.5119   $154.51   $154.50   $154.50  
  7 purchase totals = $799.40       $869.6286   $869.63   $869.60   $869.70