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 $52.60   6.544%   $56.0421   $56.04   $56.05   $56.00  
  Purchase #2 $32.35   12.732%   $36.4688   $36.47   $36.45   $36.50  
  Purchase #3 $168.39   4.792%   $176.4592   $176.46   $176.45   $176.50  
  Purchase #4 $95.31   3.564%   $98.7068   $98.71   $98.70   $98.70  
  Purchase #5 $227.57   3.428%   $235.3711   $235.37   $235.35   $235.40  
  Purchase #6 $53.58   8.149%   $57.9462   $57.95   $57.95   $57.90  
  Purchase #7 $222.81   5.173%   $234.336   $234.34   $234.35   $234.30  
  7 purchase totals = $852.61       $895.3302   $895.34   $895.30   $895.30