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 $65.81   13.632%   $74.7812   $74.78   $74.80   $74.80  
  Purchase #2 $49.75   13.253%   $56.3434   $56.34   $56.35   $56.30  
  Purchase #3 $200.62   12.158%   $225.0114   $225.01   $225.00   $225.00  
  Purchase #4 $154.40   8.199%   $167.0593   $167.06   $167.05   $167.10  
  Purchase #5 $163.87   7.501%   $176.1619   $176.16   $176.15   $176.20  
  Purchase #6 $104.65   12.147%   $117.3618   $117.36   $117.35   $117.40  
  Purchase #7 $208.75   9.208%   $227.9717   $227.97   $227.95   $228.00  
  7 purchase totals = $947.85       $1,044.6907   $1,044.68   $1,044.65   $1,044.80