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 $118.60   6.757%   $126.6138   $126.61   $126.60   $126.60  
  Purchase #2 $29.36   4.799%   $30.769   $30.77   $30.75   $30.80  
  Purchase #3 $22.55   6.632%   $24.0455   $24.05   $24.05   $24.00  
  Purchase #4 $77.25   10.576%   $85.42   $85.42   $85.40   $85.40  
  Purchase #5 $74.71   7.393%   $80.2333   $80.23   $80.25   $80.20  
  Purchase #6 $19.95   12.690%   $22.4817   $22.48   $22.50   $22.50  
  Purchase #7 $53.42   6.616%   $56.9543   $56.95   $56.95   $57.00  
  7 purchase totals = $395.84       $426.5176   $426.51   $426.50   $426.50