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 $153.73   7.425%   $165.1445   $165.14   $165.15   $165.10  
  Purchase #2 $179.63   11.861%   $200.9359   $200.94   $200.95   $200.90  
  Purchase #3 $17.95   13.708%   $20.4106   $20.41   $20.40   $20.40  
  Purchase #4 $151.26   10.377%   $166.9563   $166.96   $166.95   $167.00  
  Purchase #5 $237.99   11.770%   $266.0014   $266.00   $266.00   $266.00  
  Purchase #6 $92.78   13.517%   $105.3211   $105.32   $105.30   $105.30  
  Purchase #7 $163.30   7.156%   $174.9857   $174.99   $175.00   $175.00  
  7 purchase totals = $996.64       $1,099.7555   $1,099.76   $1,099.75   $1,099.70