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 $180.38   11.873%   $201.7965   $201.80   $201.80   $201.80  
  Purchase #2 $71.99   10.621%   $79.6361   $79.64   $79.65   $79.60  
  Purchase #3 $28.29   7.792%   $30.4944   $30.49   $30.50   $30.50  
  Purchase #4 $153.90   10.148%   $169.5178   $169.52   $169.50   $169.50  
  Purchase #5 $231.77   8.815%   $252.2005   $252.20   $252.20   $252.20  
  Purchase #6 $185.45   9.724%   $203.4832   $203.48   $203.50   $203.50  
  Purchase #7 $159.27   3.563%   $164.9448   $164.94   $164.95   $164.90  
  7 purchase totals = $1,011.05       $1,102.0733   $1,102.07   $1,102.10   $1,102.00