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 $87.55   9.501%   $95.8681   $95.87   $95.85   $95.90  
  Purchase #2 $207.87   3.305%   $214.7401   $214.74   $214.75   $214.70  
  Purchase #3 $6.35   11.712%   $7.0937   $7.09   $7.10   $7.10  
  Purchase #4 $94.25   12.536%   $106.0652   $106.07   $106.05   $106.10  
  Purchase #5 $63.57   4.363%   $66.3436   $66.34   $66.35   $66.30  
  Purchase #6 $229.72   6.231%   $244.0339   $244.03   $244.05   $244.00  
  Purchase #7 $134.87   7.224%   $144.613   $144.61   $144.60   $144.60  
  7 purchase totals = $824.18       $878.7576   $878.75   $878.75   $878.70