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 $154.68   13.622%   $175.7505   $175.75   $175.75   $175.80  
  Purchase #2 $151.85   11.524%   $169.3492   $169.35   $169.35   $169.30  
  Purchase #3 $21.63   10.616%   $23.9262   $23.93   $23.95   $23.90  
  Purchase #4 $38.67   13.309%   $43.8166   $43.82   $43.80   $43.80  
  Purchase #5 $64.91   7.174%   $69.5666   $69.57   $69.55   $69.60  
  Purchase #6 $9.41   8.347%   $10.1955   $10.20   $10.20   $10.20  
  Purchase #7 $183.26   9.145%   $200.0191   $200.02   $200.00   $200.00  
  7 purchase totals = $624.41       $692.6237   $692.64   $692.60   $692.60