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 $178.51   9.205%   $194.9418   $194.94   $194.95   $194.90  
  Purchase #2 $32.77   6.656%   $34.9512   $34.95   $34.95   $35.00  
  Purchase #3 $233.74   8.705%   $254.0871   $254.09   $254.10   $254.10  
  Purchase #4 $149.30   7.852%   $161.023   $161.02   $161.00   $161.00  
  Purchase #5 $90.44   6.702%   $96.5013   $96.50   $96.50   $96.50  
  Purchase #6 $6.90   10.423%   $7.6192   $7.62   $7.60   $7.60  
  Purchase #7 $178.59   8.453%   $193.6862   $193.69   $193.70   $193.70  
  7 purchase totals = $870.25       $942.8098   $942.81   $942.80   $942.80