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 $177.33   13.624%   $201.4894   $201.49   $201.50   $201.50  
  Purchase #2 $5.34   11.238%   $5.9401   $5.94   $5.95   $5.90  
  Purchase #3 $104.59   11.818%   $116.9504   $116.95   $116.95   $117.00  
  Purchase #4 $207.58   9.134%   $226.5404   $226.54   $226.55   $226.50  
  Purchase #5 $13.92   5.806%   $14.7282   $14.73   $14.75   $14.70  
  Purchase #6 $227.94   3.534%   $235.9954   $236.00   $236.00   $236.00  
  Purchase #7 $213.85   9.558%   $234.2898   $234.29   $234.30   $234.30  
  7 purchase totals = $950.55       $1,035.9337   $1,035.94   $1,036.00   $1,035.90