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 $61.97   3.360%   $64.0522   $64.05   $64.05   $64.10  
  Purchase #2 $178.83   11.783%   $199.9015   $199.90   $199.90   $199.90  
  Purchase #3 $119.37   3.477%   $123.5205   $123.52   $123.50   $123.50  
  Purchase #4 $33.87   3.679%   $35.1161   $35.12   $35.10   $35.10  
  Purchase #5 $65.60   13.628%   $74.54   $74.54   $74.55   $74.50  
  Purchase #6 $55.34   6.252%   $58.7999   $58.80   $58.80   $58.80  
  Purchase #7 $185.74   4.354%   $193.8271   $193.83   $193.85   $193.80  
  7 purchase totals = $700.72       $749.7573   $749.76   $749.75   $749.70