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 $173.67   6.335%   $184.672   $184.67   $184.65   $184.70  
  Purchase #2 $70.33   11.848%   $78.6627   $78.66   $78.65   $78.70  
  Purchase #3 $59.84   6.163%   $63.5279   $63.53   $63.55   $63.50  
  Purchase #4 $168.30   8.140%   $181.9996   $182.00   $182.00   $182.00  
  Purchase #5 $178.30   12.737%   $201.0101   $201.01   $201.00   $201.00  
  Purchase #6 $177.64   6.388%   $188.9876   $188.99   $189.00   $189.00  
  Purchase #7 $114.39   8.787%   $124.4414   $124.44   $124.45   $124.40  
  7 purchase totals = $942.47       $1,023.3013   $1,023.30   $1,023.30   $1,023.30