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 $67.81   12.869%   $76.5365   $76.54   $76.55   $76.50  
  Purchase #2 $112.93   5.366%   $118.9898   $118.99   $119.00   $119.00  
  Purchase #3 $204.95   8.575%   $222.5245   $222.52   $222.50   $222.50  
  Purchase #4 $181.60   7.276%   $194.8132   $194.81   $194.80   $194.80  
  Purchase #5 $99.86   11.704%   $111.5476   $111.55   $111.55   $111.50  
  Purchase #6 $208.57   10.316%   $230.0861   $230.09   $230.10   $230.10  
  Purchase #7 $44.49   12.292%   $49.9587   $49.96   $49.95   $50.00  
  7 purchase totals = $920.21       $1,004.4564   $1,004.46   $1,004.45   $1,004.40