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 $61.39   9.110%   $66.9826   $66.98   $67.00   $67.00  
  Purchase #2 $113.77   10.394%   $125.5953   $125.60   $125.60   $125.60  
  Purchase #3 $206.69   13.683%   $234.9714   $234.97   $234.95   $235.00  
  Purchase #4 $213.72   7.418%   $229.5737   $229.57   $229.55   $229.60  
  Purchase #5 $161.53   9.379%   $176.6799   $176.68   $176.70   $176.70  
  Purchase #6 $84.36   6.289%   $89.6654   $89.67   $89.65   $89.70  
  Purchase #7 $150.27   3.157%   $155.014   $155.01   $155.00   $155.00  
  7 purchase totals = $991.73       $1,078.4823   $1,078.48   $1,078.45   $1,078.60