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 $39.43   4.443%   $41.1819   $41.18   $41.20   $41.20  
  Purchase #2 $162.83   8.253%   $176.2684   $176.27   $176.25   $176.30  
  Purchase #3 $25.89   4.500%   $27.0551   $27.06   $27.05   $27.10  
  Purchase #4 $234.58   3.821%   $243.5433   $243.54   $243.55   $243.50  
  Purchase #5 $33.59   6.260%   $35.6927   $35.69   $35.70   $35.70  
  Purchase #6 $166.98   13.144%   $188.9279   $188.93   $188.95   $188.90  
  Purchase #7 $10.54   6.644%   $11.2403   $11.24   $11.25   $11.20  
  7 purchase totals = $673.84       $723.9096   $723.91   $723.95   $723.90