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 $87.52   12.850%   $98.7663   $98.77   $98.75   $98.80  
  Purchase #2 $154.66   13.435%   $175.4386   $175.44   $175.45   $175.40  
  Purchase #3 $113.48   9.293%   $124.0257   $124.03   $124.05   $124.00  
  Purchase #4 $226.57   5.868%   $239.8651   $239.87   $239.85   $239.90  
  Purchase #5 $187.91   10.693%   $208.0032   $208.00   $208.00   $208.00  
  Purchase #6 $95.72   10.133%   $105.4193   $105.42   $105.40   $105.40  
  Purchase #7 $186.83   9.423%   $204.435   $204.44   $204.45   $204.40  
  7 purchase totals = $1,052.69       $1,155.9532   $1,155.97   $1,155.95   $1,155.90