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 $232.37   11.179%   $258.3466   $258.35   $258.35   $258.30  
  Purchase #2 $88.48   10.326%   $97.6164   $97.62   $97.60   $97.60  
  Purchase #3 $30.76   7.565%   $33.087   $33.09   $33.10   $33.10  
  Purchase #4 $116.91   4.118%   $121.7244   $121.72   $121.70   $121.70  
  Purchase #5 $245.93   8.587%   $267.048   $267.05   $267.05   $267.00  
  Purchase #6 $231.40   6.110%   $245.5385   $245.54   $245.55   $245.50  
  Purchase #7 $48.36   3.184%   $49.8998   $49.90   $49.90   $49.90  
  7 purchase totals = $994.21       $1,073.2607   $1,073.27   $1,073.25   $1,073.10