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 $244.29   10.194%   $269.1929   $269.19   $269.20   $269.20  
  Purchase #2 $219.53   13.125%   $248.3433   $248.34   $248.35   $248.30  
  Purchase #3 $205.91   8.545%   $223.505   $223.51   $223.50   $223.50  
  Purchase #4 $195.51   9.791%   $214.6524   $214.65   $214.65   $214.70  
  Purchase #5 $33.52   6.426%   $35.674   $35.67   $35.65   $35.70  
  Purchase #6 $110.91   6.431%   $118.0426   $118.04   $118.05   $118.00  
  Purchase #7 $193.68   7.780%   $208.7483   $208.75   $208.75   $208.70  
  7 purchase totals = $1,203.35       $1,318.1585   $1,318.15   $1,318.15   $1,318.10