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 $165.94   11.277%   $184.6531   $184.65   $184.65   $184.70  
  Purchase #2 $98.93   13.181%   $111.97   $111.97   $111.95   $112.00  
  Purchase #3 $197.37   5.858%   $208.9319   $208.93   $208.95   $208.90  
  Purchase #4 $95.74   12.636%   $107.8377   $107.84   $107.85   $107.80  
  Purchase #5 $225.99   11.564%   $252.1235   $252.12   $252.10   $252.10  
  Purchase #6 $138.57   4.724%   $145.116   $145.12   $145.10   $145.10  
  Purchase #7 $117.49   7.827%   $126.6859   $126.69   $126.70   $126.70  
  7 purchase totals = $1,040.03       $1,137.3181   $1,137.32   $1,137.30   $1,137.30