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 $76.91   7.304%   $82.5275   $82.53   $82.55   $82.50  
  Purchase #2 $158.86   11.272%   $176.7667   $176.77   $176.75   $176.80  
  Purchase #3 $84.58   6.187%   $89.813   $89.81   $89.80   $89.80  
  Purchase #4 $31.30   10.265%   $34.5129   $34.51   $34.50   $34.50  
  Purchase #5 $217.58   9.698%   $238.6809   $238.68   $238.70   $238.70  
  Purchase #6 $220.91   11.783%   $246.9398   $246.94   $246.95   $246.90  
  Purchase #7 $135.26   3.693%   $140.2552   $140.26   $140.25   $140.30  
  7 purchase totals = $925.40       $1,009.4960   $1,009.50   $1,009.50   $1,009.50