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 $58.62   5.363%   $61.7638   $61.76   $61.75   $61.80  
  Purchase #2 $33.58   6.393%   $35.7268   $35.73   $35.75   $35.70  
  Purchase #3 $224.77   4.382%   $234.6194   $234.62   $234.60   $234.60  
  Purchase #4 $53.91   9.143%   $58.839   $58.84   $58.85   $58.80  
  Purchase #5 $157.83   3.730%   $163.7171   $163.72   $163.70   $163.70  
  Purchase #6 $67.39   10.263%   $74.3062   $74.31   $74.30   $74.30  
  Purchase #7 $172.73   7.708%   $186.044   $186.04   $186.05   $186.00  
  7 purchase totals = $768.83       $815.0163   $815.02   $815.00   $814.90