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 $143.88   13.117%   $162.7527   $162.75   $162.75   $162.80  
  Purchase #2 $157.34   9.495%   $172.2794   $172.28   $172.30   $172.30  
  Purchase #3 $10.25   4.359%   $10.6968   $10.70   $10.70   $10.70  
  Purchase #4 $203.98   10.315%   $225.0205   $225.02   $225.00   $225.00  
  Purchase #5 $85.29   3.405%   $88.1941   $88.19   $88.20   $88.20  
  Purchase #6 $127.55   5.604%   $134.6979   $134.70   $134.70   $134.70  
  Purchase #7 $188.83   6.856%   $201.7762   $201.78   $201.80   $201.80  
  7 purchase totals = $917.12       $995.4176   $995.42   $995.45   $995.50