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 $244.58   8.383%   $265.0831   $265.08   $265.10   $265.10  
  Purchase #2 $211.55   13.127%   $239.3202   $239.32   $239.30   $239.30  
  Purchase #3 $157.82   10.793%   $174.8535   $174.85   $174.85   $174.90  
  Purchase #4 $88.46   10.121%   $97.413   $97.41   $97.40   $97.40  
  Purchase #5 $121.82   12.791%   $137.402   $137.40   $137.40   $137.40  
  Purchase #6 $147.35   11.322%   $164.033   $164.03   $164.05   $164.00  
  Purchase #7 $69.42   10.544%   $76.7396   $76.74   $76.75   $76.70  
  7 purchase totals = $1,041.00       $1,154.8444   $1,154.83   $1,154.85   $1,154.80