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 $33.41   13.767%   $38.0096   $38.01   $38.00   $38.00  
  Purchase #2 $219.98   6.346%   $233.9399   $233.94   $233.95   $233.90  
  Purchase #3 $119.70   6.581%   $127.5775   $127.58   $127.60   $127.60  
  Purchase #4 $51.77   6.660%   $55.2179   $55.22   $55.20   $55.20  
  Purchase #5 $47.33   11.497%   $52.7715   $52.77   $52.75   $52.80  
  Purchase #6 $166.74   5.849%   $176.4926   $176.49   $176.50   $176.50  
  Purchase #7 $7.54   7.255%   $8.087   $8.09   $8.10   $8.10  
  7 purchase totals = $646.47       $692.0960   $692.10   $692.10   $692.10