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 $245.95   8.512%   $266.8853   $266.89   $266.90   $266.90  
  Purchase #2 $31.53   11.277%   $35.0856   $35.09   $35.10   $35.10  
  Purchase #3 $184.47   4.613%   $192.9796   $192.98   $193.00   $193.00  
  Purchase #4 $193.73   4.256%   $201.9751   $201.98   $202.00   $202.00  
  Purchase #5 $115.49   10.147%   $127.2088   $127.21   $127.20   $127.20  
  Purchase #6 $129.37   10.853%   $143.4105   $143.41   $143.40   $143.40  
  Purchase #7 $225.73   4.628%   $236.1768   $236.18   $236.20   $236.20  
  7 purchase totals = $1,126.27       $1,203.7217   $1,203.74   $1,203.80   $1,203.80