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 $29.66   11.471%   $33.0623   $33.06   $33.05   $33.10  
  Purchase #2 $176.58   5.408%   $186.1294   $186.13   $186.15   $186.10  
  Purchase #3 $162.98   8.405%   $176.6785   $176.68   $176.70   $176.70  
  Purchase #4 $6.74   4.427%   $7.0384   $7.04   $7.05   $7.00  
  Purchase #5 $116.27   9.604%   $127.4366   $127.44   $127.45   $127.40  
  Purchase #6 $129.44   8.511%   $140.4566   $140.46   $140.45   $140.50  
  Purchase #7 $207.89   7.160%   $222.7749   $222.77   $222.75   $222.80  
  7 purchase totals = $829.56       $893.5767   $893.58   $893.60   $893.60