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 $204.50   10.565%   $226.1054   $226.11   $226.10   $226.10  
  Purchase #2 $217.93   11.743%   $243.5215   $243.52   $243.50   $243.50  
  Purchase #3 $158.56   7.150%   $169.897   $169.90   $169.90   $169.90  
  Purchase #4 $101.75   12.241%   $114.2052   $114.21   $114.20   $114.20  
  Purchase #5 $191.63   3.825%   $198.9598   $198.96   $198.95   $199.00  
  Purchase #6 $155.65   4.845%   $163.1912   $163.19   $163.20   $163.20  
  Purchase #7 $236.26   13.546%   $268.2638   $268.26   $268.25   $268.30  
  7 purchase totals = $1,266.28       $1,384.1439   $1,384.15   $1,384.10   $1,384.20