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 $53.68   5.861%   $56.8262   $56.83   $56.85   $56.80  
  Purchase #2 $118.47   8.288%   $128.2888   $128.29   $128.30   $128.30  
  Purchase #3 $218.80   13.451%   $248.2308   $248.23   $248.25   $248.20  
  Purchase #4 $123.87   12.382%   $139.2076   $139.21   $139.20   $139.20  
  Purchase #5 $116.85   4.712%   $122.356   $122.36   $122.35   $122.40  
  Purchase #6 $112.55   8.671%   $122.3092   $122.31   $122.30   $122.30  
  Purchase #7 $172.46   4.661%   $180.4984   $180.50   $180.50   $180.50  
  7 purchase totals = $916.68       $997.7170   $997.73   $997.75   $997.70