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 $62.83   4.778%   $65.832   $65.83   $65.85   $65.80  
  Purchase #2 $221.94   8.605%   $241.0379   $241.04   $241.05   $241.00  
  Purchase #3 $189.56   12.196%   $212.6787   $212.68   $212.70   $212.70  
  Purchase #4 $141.61   11.277%   $157.5794   $157.58   $157.60   $157.60  
  Purchase #5 $226.49   3.321%   $234.0117   $234.01   $234.00   $234.00  
  Purchase #6 $38.89   12.199%   $43.6342   $43.63   $43.65   $43.60  
  Purchase #7 $42.49   9.561%   $46.5525   $46.55   $46.55   $46.60  
  7 purchase totals = $923.81       $1,001.3264   $1,001.32   $1,001.40   $1,001.30