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 $205.75   8.712%   $223.6749   $223.67   $223.65   $223.70  
  Purchase #2 $113.50   11.673%   $126.7489   $126.75   $126.75   $126.70  
  Purchase #3 $123.89   7.776%   $133.5237   $133.52   $133.50   $133.50  
  Purchase #4 $239.50   5.711%   $253.1778   $253.18   $253.20   $253.20  
  Purchase #5 $246.61   3.479%   $255.1896   $255.19   $255.20   $255.20  
  Purchase #6 $97.73   5.517%   $103.1218   $103.12   $103.10   $103.10  
  Purchase #7 $239.96   3.417%   $248.1594   $248.16   $248.15   $248.20  
  7 purchase totals = $1,266.94       $1,343.5961   $1,343.59   $1,343.55   $1,343.60