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 $58.63   11.836%   $65.5694   $65.57   $65.55   $65.60  
  Purchase #2 $89.34   8.784%   $97.1876   $97.19   $97.20   $97.20  
  Purchase #3 $221.95   12.613%   $249.9446   $249.94   $249.95   $249.90  
  Purchase #4 $200.96   5.332%   $211.6752   $211.68   $211.70   $211.70  
  Purchase #5 $169.26   7.349%   $181.6989   $181.70   $181.70   $181.70  
  Purchase #6 $238.72   11.873%   $267.0632   $267.06   $267.05   $267.10  
  Purchase #7 $208.66   8.360%   $226.104   $226.10   $226.10   $226.10  
  7 purchase totals = $1,187.52       $1,299.2429   $1,299.24   $1,299.25   $1,299.30