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 $64.50   5.491%   $68.0417   $68.04   $68.05   $68.00  
  Purchase #2 $148.37   13.871%   $168.9504   $168.95   $168.95   $169.00  
  Purchase #3 $128.52   6.110%   $136.3726   $136.37   $136.35   $136.40  
  Purchase #4 $163.30   11.275%   $181.7121   $181.71   $181.70   $181.70  
  Purchase #5 $50.39   12.775%   $56.8273   $56.83   $56.85   $56.80  
  Purchase #6 $185.84   3.557%   $192.4503   $192.45   $192.45   $192.50  
  Purchase #7 $83.96   8.856%   $91.3955   $91.40   $91.40   $91.40  
  7 purchase totals = $824.88       $895.7499   $895.75   $895.75   $895.80