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 $144.73   13.248%   $163.9038   $163.90   $163.90   $163.90  
  Purchase #2 $168.88   3.613%   $174.9816   $174.98   $175.00   $175.00  
  Purchase #3 $44.96   4.663%   $47.0565   $47.06   $47.05   $47.10  
  Purchase #4 $181.92   9.348%   $198.9259   $198.93   $198.95   $198.90  
  Purchase #5 $94.92   13.705%   $107.9288   $107.93   $107.95   $107.90  
  Purchase #6 $105.30   10.595%   $116.4565   $116.46   $116.45   $116.50  
  Purchase #7 $81.26   4.278%   $84.7363   $84.74   $84.75   $84.70  
  7 purchase totals = $821.97       $893.9894   $894.00   $894.05   $894.00