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 $40.37   6.542%   $43.011   $43.01   $43.00   $43.00  
  Purchase #2 $208.62   6.349%   $221.8653   $221.87   $221.85   $221.90  
  Purchase #3 $37.44   9.429%   $40.9702   $40.97   $40.95   $41.00  
  Purchase #4 $89.86   4.233%   $93.6638   $93.66   $93.65   $93.70  
  Purchase #5 $165.65   7.441%   $177.976   $177.98   $178.00   $178.00  
  Purchase #6 $222.99   10.235%   $245.813   $245.81   $245.80   $245.80  
  Purchase #7 $178.64   8.295%   $193.4582   $193.46   $193.45   $193.50  
  7 purchase totals = $943.57       $1,016.7575   $1,016.76   $1,016.70   $1,016.90