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 $102.92   13.648%   $116.9665   $116.97   $116.95   $117.00  
  Purchase #2 $233.44   13.772%   $265.5894   $265.59   $265.60   $265.60  
  Purchase #3 $176.34   11.411%   $196.4622   $196.46   $196.45   $196.50  
  Purchase #4 $25.58   5.748%   $27.0503   $27.05   $27.05   $27.10  
  Purchase #5 $230.28   11.342%   $256.3984   $256.40   $256.40   $256.40  
  Purchase #6 $103.39   11.712%   $115.499   $115.50   $115.50   $115.50  
  Purchase #7 $76.41   4.689%   $79.9929   $79.99   $80.00   $80.00  
  7 purchase totals = $948.36       $1,057.9587   $1,057.96   $1,057.95   $1,058.10