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 $192.66   5.676%   $203.5954   $203.60   $203.60   $203.60  
  Purchase #2 $156.54   7.572%   $168.3932   $168.39   $168.40   $168.40  
  Purchase #3 $135.72   5.713%   $143.4737   $143.47   $143.45   $143.50  
  Purchase #4 $63.27   5.830%   $66.9586   $66.96   $66.95   $67.00  
  Purchase #5 $49.96   9.124%   $54.5184   $54.52   $54.50   $54.50  
  Purchase #6 $113.45   10.637%   $125.5177   $125.52   $125.50   $125.50  
  Purchase #7 $248.38   6.832%   $265.3493   $265.35   $265.35   $265.30  
  7 purchase totals = $959.98       $1,027.8063   $1,027.81   $1,027.75   $1,027.80