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 $60.62   4.386%   $63.2788   $63.28   $63.30   $63.30  
  Purchase #2 $215.83   9.605%   $236.5605   $236.56   $236.55   $236.60  
  Purchase #3 $242.56   8.579%   $263.3692   $263.37   $263.35   $263.40  
  Purchase #4 $49.90   10.611%   $55.1949   $55.19   $55.20   $55.20  
  Purchase #5 $223.48   8.739%   $243.0099   $243.01   $243.00   $243.00  
  Purchase #6 $135.74   11.259%   $151.023   $151.02   $151.00   $151.00  
  Purchase #7 $227.86   6.806%   $243.3682   $243.37   $243.35   $243.40  
  7 purchase totals = $1,155.99       $1,255.8045   $1,255.80   $1,255.75   $1,255.90