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 $196.26   9.210%   $214.3355   $214.34   $214.35   $214.30  
  Purchase #2 $117.41   6.174%   $124.6589   $124.66   $124.65   $124.70  
  Purchase #3 $244.68   13.860%   $278.5926   $278.59   $278.60   $278.60  
  Purchase #4 $226.65   6.579%   $241.5613   $241.56   $241.55   $241.60  
  Purchase #5 $245.31   3.492%   $253.8762   $253.88   $253.90   $253.90  
  Purchase #6 $147.53   11.584%   $164.6199   $164.62   $164.60   $164.60  
  Purchase #7 $36.33   10.820%   $40.2609   $40.26   $40.25   $40.30  
  7 purchase totals = $1,214.17       $1,317.9053   $1,317.91   $1,317.90   $1,318.00