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 $168.65   9.263%   $184.272   $184.27   $184.25   $184.30  
  Purchase #2 $67.91   8.179%   $73.4644   $73.46   $73.45   $73.50  
  Purchase #3 $211.28   13.552%   $239.9127   $239.91   $239.90   $239.90  
  Purchase #4 $234.97   6.556%   $250.3746   $250.37   $250.35   $250.40  
  Purchase #5 $104.73   7.792%   $112.8906   $112.89   $112.90   $112.90  
  Purchase #6 $167.91   8.388%   $181.9943   $181.99   $182.00   $182.00  
  Purchase #7 $86.78   8.474%   $94.1337   $94.13   $94.15   $94.10  
  7 purchase totals = $1,042.23       $1,137.0423   $1,137.02   $1,137.00   $1,137.10