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 $105.53   11.761%   $117.9414   $117.94   $117.95   $117.90  
  Purchase #2 $192.76   4.440%   $201.3185   $201.32   $201.30   $201.30  
  Purchase #3 $56.55   3.551%   $58.5581   $58.56   $58.55   $58.60  
  Purchase #4 $34.30   5.569%   $36.2102   $36.21   $36.20   $36.20  
  Purchase #5 $152.60   13.338%   $172.9538   $172.95   $172.95   $173.00  
  Purchase #6 $22.44   3.391%   $23.2009   $23.20   $23.20   $23.20  
  Purchase #7 $32.96   10.102%   $36.2896   $36.29   $36.30   $36.30  
  7 purchase totals = $597.14       $646.4725   $646.47   $646.45   $646.50