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 $130.59   8.548%   $141.7528   $141.75   $141.75   $141.80  
  Purchase #2 $25.25   3.680%   $26.1792   $26.18   $26.20   $26.20  
  Purchase #3 $227.76   8.579%   $247.2995   $247.30   $247.30   $247.30  
  Purchase #4 $158.51   11.705%   $177.0636   $177.06   $177.05   $177.10  
  Purchase #5 $8.33   4.141%   $8.6749   $8.67   $8.65   $8.70  
  Purchase #6 $229.98   5.710%   $243.1119   $243.11   $243.10   $243.10  
  Purchase #7 $223.40   11.419%   $248.91   $248.91   $248.90   $248.90  
  7 purchase totals = $1,003.82       $1,092.9919   $1,092.98   $1,092.95   $1,093.10