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 $243.67   9.681%   $267.2597   $267.26   $267.25   $267.30  
  Purchase #2 $176.72   7.253%   $189.5375   $189.54   $189.55   $189.50  
  Purchase #3 $38.44   10.758%   $42.5754   $42.58   $42.60   $42.60  
  Purchase #4 $250.96   7.552%   $269.9125   $269.91   $269.90   $269.90  
  Purchase #5 $231.94   3.837%   $240.8395   $240.84   $240.85   $240.80  
  Purchase #6 $10.80   5.174%   $11.3588   $11.36   $11.35   $11.40  
  Purchase #7 $178.70   13.152%   $202.2026   $202.20   $202.20   $202.20  
  7 purchase totals = $1,131.23       $1,223.6860   $1,223.69   $1,223.70   $1,223.70