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 $111.26   10.853%   $123.335   $123.34   $123.35   $123.30  
  Purchase #2 $31.36   11.521%   $34.973   $34.97   $34.95   $35.00  
  Purchase #3 $242.54   4.278%   $252.9159   $252.92   $252.90   $252.90  
  Purchase #4 $175.83   8.519%   $190.809   $190.81   $190.80   $190.80  
  Purchase #5 $243.81   10.157%   $268.5738   $268.57   $268.55   $268.60  
  Purchase #6 $67.80   10.285%   $74.7732   $74.77   $74.75   $74.80  
  Purchase #7 $9.36   9.714%   $10.2692   $10.27   $10.25   $10.30  
  7 purchase totals = $881.96       $955.6491   $955.65   $955.55   $955.70