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 $31.67   8.291%   $34.2958   $34.30   $34.30   $34.30  
  Purchase #2 $240.27   6.572%   $256.0605   $256.06   $256.05   $256.10  
  Purchase #3 $190.61   12.265%   $213.9883   $213.99   $214.00   $214.00  
  Purchase #4 $225.60   3.526%   $233.5547   $233.55   $233.55   $233.60  
  Purchase #5 $83.83   8.670%   $91.0981   $91.10   $91.10   $91.10  
  Purchase #6 $176.91   6.168%   $187.8218   $187.82   $187.80   $187.80  
  Purchase #7 $25.72   7.541%   $27.6595   $27.66   $27.65   $27.70  
  7 purchase totals = $974.61       $1,044.4787   $1,044.48   $1,044.45   $1,044.60