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 $66.83   5.204%   $70.3078   $70.31   $70.30   $70.30  
  Purchase #2 $164.29   13.244%   $186.0486   $186.05   $186.05   $186.00  
  Purchase #3 $89.41   8.146%   $96.6933   $96.69   $96.70   $96.70  
  Purchase #4 $172.48   10.394%   $190.4076   $190.41   $190.40   $190.40  
  Purchase #5 $56.79   9.103%   $61.9596   $61.96   $61.95   $62.00  
  Purchase #6 $190.61   11.347%   $212.2385   $212.24   $212.25   $212.20  
  Purchase #7 $157.77   5.818%   $166.9491   $166.95   $166.95   $166.90  
  7 purchase totals = $898.18       $984.6045   $984.61   $984.60   $984.50