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 $239.81   10.619%   $265.2754   $265.28   $265.30   $265.30  
  Purchase #2 $225.85   7.740%   $243.3308   $243.33   $243.35   $243.30  
  Purchase #3 $88.91   5.593%   $93.8827   $93.88   $93.90   $93.90  
  Purchase #4 $181.83   11.691%   $203.0877   $203.09   $203.10   $203.10  
  Purchase #5 $69.45   4.765%   $72.7593   $72.76   $72.75   $72.80  
  Purchase #6 $189.30   12.617%   $213.184   $213.18   $213.20   $213.20  
  Purchase #7 $238.35   10.508%   $263.3958   $263.40   $263.40   $263.40  
  7 purchase totals = $1,233.50       $1,354.9157   $1,354.92   $1,355.00   $1,355.00