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 $65.47   4.362%   $68.3258   $68.33   $68.35   $68.30  
  Purchase #2 $159.69   11.180%   $177.5433   $177.54   $177.55   $177.50  
  Purchase #3 $128.37   9.426%   $140.4702   $140.47   $140.45   $140.50  
  Purchase #4 $95.25   11.460%   $106.1657   $106.17   $106.15   $106.20  
  Purchase #5 $69.41   7.201%   $74.4082   $74.41   $74.40   $74.40  
  Purchase #6 $143.52   8.169%   $155.2441   $155.24   $155.25   $155.20  
  Purchase #7 $21.88   3.796%   $22.7106   $22.71   $22.70   $22.70  
  7 purchase totals = $683.59       $744.8679   $744.87   $744.85   $744.80