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 $221.69   10.763%   $245.5505   $245.55   $245.55   $245.60  
  Purchase #2 $181.36   13.155%   $205.2179   $205.22   $205.20   $205.20  
  Purchase #3 $245.51   13.483%   $278.6121   $278.61   $278.60   $278.60  
  Purchase #4 $123.27   4.291%   $128.5595   $128.56   $128.55   $128.60  
  Purchase #5 $28.37   11.477%   $31.626   $31.63   $31.65   $31.60  
  Purchase #6 $28.29   8.739%   $30.7623   $30.76   $30.75   $30.80  
  Purchase #7 $139.69   9.377%   $152.7887   $152.79   $152.80   $152.80  
  7 purchase totals = $968.18       $1,073.1170   $1,073.12   $1,073.10   $1,073.20