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 $206.48   8.654%   $224.3488   $224.35   $224.35   $224.30  
  Purchase #2 $116.57   13.383%   $132.1706   $132.17   $132.15   $132.20  
  Purchase #3 $99.67   13.710%   $113.3348   $113.33   $113.35   $113.30  
  Purchase #4 $213.58   5.170%   $224.6221   $224.62   $224.60   $224.60  
  Purchase #5 $96.35   6.195%   $102.3189   $102.32   $102.30   $102.30  
  Purchase #6 $91.36   6.536%   $97.3313   $97.33   $97.35   $97.30  
  Purchase #7 $174.49   7.320%   $187.2627   $187.26   $187.25   $187.30  
  7 purchase totals = $998.50       $1,081.3892   $1,081.38   $1,081.35   $1,081.30