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 $219.48   3.283%   $226.6855   $226.69   $226.70   $226.70  
  Purchase #2 $220.39   4.728%   $230.81   $230.81   $230.80   $230.80  
  Purchase #3 $53.93   6.451%   $57.409   $57.41   $57.40   $57.40  
  Purchase #4 $122.40   8.261%   $132.5115   $132.51   $132.50   $132.50  
  Purchase #5 $80.31   6.209%   $85.2964   $85.30   $85.30   $85.30  
  Purchase #6 $192.96   10.432%   $213.0896   $213.09   $213.10   $213.10  
  Purchase #7 $81.93   12.297%   $92.0049   $92.00   $92.00   $92.00  
  7 purchase totals = $971.40       $1,037.8069   $1,037.81   $1,037.80   $1,037.80