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 $62.51   11.317%   $69.5843   $69.58   $69.60   $69.60  
  Purchase #2 $227.31   6.268%   $241.5578   $241.56   $241.55   $241.60  
  Purchase #3 $67.37   4.793%   $70.599   $70.60   $70.60   $70.60  
  Purchase #4 $161.33   13.483%   $183.0821   $183.08   $183.10   $183.10  
  Purchase #5 $130.92   6.591%   $139.5489   $139.55   $139.55   $139.50  
  Purchase #6 $209.44   10.535%   $231.5045   $231.50   $231.50   $231.50  
  Purchase #7 $41.33   13.264%   $46.812   $46.81   $46.80   $46.80  
  7 purchase totals = $900.21       $982.6886   $982.68   $982.70   $982.70