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 $48.51   9.652%   $53.1922   $53.19   $53.20   $53.20  
  Purchase #2 $113.51   13.388%   $128.7067   $128.71   $128.70   $128.70  
  Purchase #3 $142.86   13.248%   $161.7861   $161.79   $161.80   $161.80  
  Purchase #4 $226.31   6.579%   $241.1989   $241.20   $241.20   $241.20  
  Purchase #5 $209.80   9.675%   $230.0982   $230.10   $230.10   $230.10  
  Purchase #6 $125.90   11.109%   $139.8862   $139.89   $139.90   $139.90  
  Purchase #7 $97.80   5.355%   $103.0372   $103.04   $103.05   $103.00  
  7 purchase totals = $964.69       $1,057.9055   $1,057.92   $1,057.95   $1,057.90