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 $52.69   13.800%   $59.9612   $59.96   $59.95   $60.00  
  Purchase #2 $156.41   6.413%   $166.4406   $166.44   $166.45   $166.40  
  Purchase #3 $33.69   8.268%   $36.4755   $36.48   $36.50   $36.50  
  Purchase #4 $177.44   4.755%   $185.8773   $185.88   $185.90   $185.90  
  Purchase #5 $186.42   9.586%   $204.2902   $204.29   $204.30   $204.30  
  Purchase #6 $11.71   11.807%   $13.0926   $13.09   $13.10   $13.10  
  Purchase #7 $109.40   3.446%   $113.1699   $113.17   $113.15   $113.20  
  7 purchase totals = $727.76       $779.3073   $779.31   $779.35   $779.40