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 $52.27   7.824%   $56.3596   $56.36   $56.35   $56.40  
  Purchase #2 $71.48   11.423%   $79.6452   $79.65   $79.65   $79.60  
  Purchase #3 $106.68   11.434%   $118.8778   $118.88   $118.90   $118.90  
  Purchase #4 $35.50   6.401%   $37.7724   $37.77   $37.75   $37.80  
  Purchase #5 $231.49   13.777%   $263.3824   $263.38   $263.40   $263.40  
  Purchase #6 $47.83   9.683%   $52.4614   $52.46   $52.45   $52.50  
  Purchase #7 $182.68   11.687%   $204.0298   $204.03   $204.05   $204.00  
  7 purchase totals = $727.93       $812.5286   $812.53   $812.55   $812.60