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 $84.62   11.123%   $94.0323   $94.03   $94.05   $94.00  
  Purchase #2 $127.30   8.614%   $138.2656   $138.27   $138.25   $138.30  
  Purchase #3 $104.48   12.255%   $117.284   $117.28   $117.30   $117.30  
  Purchase #4 $163.91   11.659%   $183.0203   $183.02   $183.00   $183.00  
  Purchase #5 $120.90   13.420%   $137.1248   $137.12   $137.10   $137.10  
  Purchase #6 $23.57   10.545%   $26.0555   $26.06   $26.05   $26.10  
  Purchase #7 $65.59   12.274%   $73.6405   $73.64   $73.65   $73.60  
  7 purchase totals = $690.37       $769.4230   $769.42   $769.40   $769.40