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 $182.81   8.379%   $198.1276   $198.13   $198.15   $198.10  
  Purchase #2 $79.85   7.668%   $85.9729   $85.97   $85.95   $86.00  
  Purchase #3 $14.42   10.288%   $15.9035   $15.90   $15.90   $15.90  
  Purchase #4 $75.38   8.545%   $81.8212   $81.82   $81.80   $81.80  
  Purchase #5 $118.74   8.288%   $128.5812   $128.58   $128.60   $128.60  
  Purchase #6 $61.72   3.142%   $63.6592   $63.66   $63.65   $63.70  
  Purchase #7 $49.71   7.737%   $53.5561   $53.56   $53.55   $53.60  
  7 purchase totals = $582.63       $627.6217   $627.62   $627.60   $627.70