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 $232.50   6.564%   $247.7613   $247.76   $247.75   $247.80  
  Purchase #2 $149.60   9.866%   $164.3595   $164.36   $164.35   $164.40  
  Purchase #3 $55.53   8.764%   $60.3966   $60.40   $60.40   $60.40  
  Purchase #4 $64.30   7.820%   $69.3283   $69.33   $69.35   $69.30  
  Purchase #5 $153.39   12.724%   $172.9073   $172.91   $172.90   $172.90  
  Purchase #6 $198.98   3.186%   $205.3195   $205.32   $205.30   $205.30  
  Purchase #7 $203.33   10.777%   $225.2429   $225.24   $225.25   $225.20  
  7 purchase totals = $1,057.63       $1,145.3154   $1,145.32   $1,145.30   $1,145.30