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 $86.64   10.230%   $95.5033   $95.50   $95.50   $95.50  
  Purchase #2 $150.75   8.507%   $163.5743   $163.57   $163.55   $163.60  
  Purchase #3 $76.39   3.496%   $79.0606   $79.06   $79.05   $79.10  
  Purchase #4 $243.99   13.809%   $277.6826   $277.68   $277.70   $277.70  
  Purchase #5 $14.98   13.602%   $17.0176   $17.02   $17.00   $17.00  
  Purchase #6 $199.56   5.493%   $210.5218   $210.52   $210.50   $210.50  
  Purchase #7 $81.38   8.241%   $88.0865   $88.09   $88.10   $88.10  
  7 purchase totals = $853.69       $931.4467   $931.44   $931.40   $931.50