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 $248.72   10.228%   $274.1591   $274.16   $274.15   $274.20  
  Purchase #2 $186.41   4.351%   $194.5207   $194.52   $194.50   $194.50  
  Purchase #3 $7.44   10.140%   $8.1944   $8.19   $8.20   $8.20  
  Purchase #4 $117.35   3.386%   $121.3235   $121.32   $121.30   $121.30  
  Purchase #5 $127.50   9.731%   $139.907   $139.91   $139.90   $139.90  
  Purchase #6 $33.81   4.566%   $35.3538   $35.35   $35.35   $35.40  
  Purchase #7 $242.72   10.847%   $269.0478   $269.05   $269.05   $269.00  
  7 purchase totals = $963.95       $1,042.5063   $1,042.50   $1,042.45   $1,042.50