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 $180.99   12.724%   $204.0192   $204.02   $204.00   $204.00  
  Purchase #2 $200.68   9.489%   $219.7225   $219.72   $219.70   $219.70  
  Purchase #3 $209.43   10.820%   $232.0903   $232.09   $232.10   $232.10  
  Purchase #4 $23.49   10.645%   $25.9905   $25.99   $26.00   $26.00  
  Purchase #5 $32.76   9.847%   $35.9859   $35.99   $36.00   $36.00  
  Purchase #6 $223.49   11.251%   $248.6349   $248.63   $248.65   $248.60  
  Purchase #7 $33.80   5.798%   $35.7597   $35.76   $35.75   $35.80  
  7 purchase totals = $904.64       $1,002.2030   $1,002.20   $1,002.20   $1,002.20