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 $30.41   4.522%   $31.7851   $31.79   $31.80   $31.80  
  Purchase #2 $204.34   12.842%   $230.5813   $230.58   $230.60   $230.60  
  Purchase #3 $114.41   12.773%   $129.0236   $129.02   $129.00   $129.00  
  Purchase #4 $35.54   13.551%   $40.356   $40.36   $40.35   $40.40  
  Purchase #5 $207.69   3.343%   $214.6331   $214.63   $214.65   $214.60  
  Purchase #6 $144.89   9.104%   $158.0808   $158.08   $158.10   $158.10  
  Purchase #7 $179.53   6.109%   $190.4975   $190.50   $190.50   $190.50  
  7 purchase totals = $916.81       $994.9574   $994.96   $995.00   $995.00