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 $84.36   12.725%   $95.0948   $95.09   $95.10   $95.10  
  Purchase #2 $243.52   9.656%   $267.0343   $267.03   $267.05   $267.00  
  Purchase #3 $47.36   4.718%   $49.5944   $49.59   $49.60   $49.60  
  Purchase #4 $92.45   6.634%   $98.5831   $98.58   $98.60   $98.60  
  Purchase #5 $63.99   5.241%   $67.3437   $67.34   $67.35   $67.30  
  Purchase #6 $63.83   6.602%   $68.0441   $68.04   $68.05   $68.00  
  Purchase #7 $37.93   8.239%   $41.0551   $41.06   $41.05   $41.10  
  7 purchase totals = $633.44       $686.7495   $686.73   $686.80   $686.70