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 $184.90   10.239%   $203.8319   $203.83   $203.85   $203.80  
  Purchase #2 $111.61   11.433%   $124.3704   $124.37   $124.35   $124.40  
  Purchase #3 $73.88   7.195%   $79.1957   $79.20   $79.20   $79.20  
  Purchase #4 $189.62   8.506%   $205.7491   $205.75   $205.75   $205.70  
  Purchase #5 $127.76   4.452%   $133.4479   $133.45   $133.45   $133.40  
  Purchase #6 $177.37   8.791%   $192.9626   $192.96   $192.95   $193.00  
  Purchase #7 $226.79   6.471%   $241.4656   $241.47   $241.45   $241.50  
  7 purchase totals = $1,091.93       $1,181.0232   $1,181.03   $1,181.00   $1,181.00