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 $61.73   12.340%   $69.3475   $69.35   $69.35   $69.30  
  Purchase #2 $222.99   8.124%   $241.1057   $241.11   $241.10   $241.10  
  Purchase #3 $34.50   4.162%   $35.9359   $35.94   $35.95   $35.90  
  Purchase #4 $85.80   7.130%   $91.9175   $91.92   $91.90   $91.90  
  Purchase #5 $92.64   5.304%   $97.5536   $97.55   $97.55   $97.60  
  Purchase #6 $67.76   11.491%   $75.5463   $75.55   $75.55   $75.50  
  Purchase #7 $23.35   11.413%   $26.0149   $26.01   $26.00   $26.00  
  7 purchase totals = $588.77       $637.4214   $637.43   $637.40   $637.30