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 $243.25   4.727%   $254.7484   $254.75   $254.75   $254.70  
  Purchase #2 $85.54   3.652%   $88.6639   $88.66   $88.65   $88.70  
  Purchase #3 $20.37   8.430%   $22.0872   $22.09   $22.10   $22.10  
  Purchase #4 $215.69   6.463%   $229.63   $229.63   $229.65   $229.60  
  Purchase #5 $42.81   13.451%   $48.5684   $48.57   $48.55   $48.60  
  Purchase #6 $181.26   6.165%   $192.4347   $192.43   $192.45   $192.40  
  Purchase #7 $54.46   7.270%   $58.4192   $58.42   $58.40   $58.40  
  7 purchase totals = $843.38       $894.5518   $894.55   $894.55   $894.50