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 $106.30   8.799%   $115.6533   $115.65   $115.65   $115.70  
  Purchase #2 $15.62   11.124%   $17.3576   $17.36   $17.35   $17.40  
  Purchase #3 $104.89   13.421%   $118.9673   $118.97   $118.95   $119.00  
  Purchase #4 $180.99   7.691%   $194.9099   $194.91   $194.90   $194.90  
  Purchase #5 $187.48   11.158%   $208.399   $208.40   $208.40   $208.40  
  Purchase #6 $105.71   7.102%   $113.2175   $113.22   $113.20   $113.20  
  Purchase #7 $207.79   10.126%   $228.8308   $228.83   $228.85   $228.80  
  7 purchase totals = $908.78       $997.3354   $997.34   $997.30   $997.40