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 $66.61   8.158%   $72.044   $72.04   $72.05   $72.00  
  Purchase #2 $45.53   9.592%   $49.8972   $49.90   $49.90   $49.90  
  Purchase #3 $48.49   7.164%   $51.9638   $51.96   $51.95   $52.00  
  Purchase #4 $205.74   9.679%   $225.6536   $225.65   $225.65   $225.70  
  Purchase #5 $171.72   12.209%   $192.6853   $192.69   $192.70   $192.70  
  Purchase #6 $122.28   7.263%   $131.1612   $131.16   $131.15   $131.20  
  Purchase #7 $18.28   10.683%   $20.2329   $20.23   $20.25   $20.20  
  7 purchase totals = $678.65       $743.6380   $743.63   $743.65   $743.70