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 $34.50   11.721%   $38.5437   $38.54   $38.55   $38.50  
  Purchase #2 $22.25   9.715%   $24.4116   $24.41   $24.40   $24.40  
  Purchase #3 $160.29   13.235%   $181.5044   $181.50   $181.50   $181.50  
  Purchase #4 $50.90   5.511%   $53.7051   $53.71   $53.70   $53.70  
  Purchase #5 $238.91   5.649%   $252.406   $252.41   $252.40   $252.40  
  Purchase #6 $66.44   3.235%   $68.5893   $68.59   $68.60   $68.60  
  Purchase #7 $79.75   7.737%   $85.9203   $85.92   $85.90   $85.90  
  7 purchase totals = $653.04       $705.0804   $705.08   $705.05   $705.00