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 $168.81   10.801%   $187.0432   $187.04   $187.05   $187.00  
  Purchase #2 $64.53   5.191%   $67.8798   $67.88   $67.90   $67.90  
  Purchase #3 $244.75   8.695%   $266.031   $266.03   $266.05   $266.00  
  Purchase #4 $69.88   9.246%   $76.3411   $76.34   $76.35   $76.30  
  Purchase #5 $106.57   10.773%   $118.0508   $118.05   $118.05   $118.10  
  Purchase #6 $190.72   5.369%   $200.9598   $200.96   $200.95   $201.00  
  Purchase #7 $82.91   5.233%   $87.2487   $87.25   $87.25   $87.20  
  7 purchase totals = $928.17       $1,003.5544   $1,003.55   $1,003.60   $1,003.50