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 $183.68   6.493%   $195.6063   $195.61   $195.60   $195.60  
  Purchase #2 $162.59   8.285%   $176.0606   $176.06   $176.05   $176.10  
  Purchase #3 $152.65   3.244%   $157.602   $157.60   $157.60   $157.60  
  Purchase #4 $40.78   11.156%   $45.3294   $45.33   $45.35   $45.30  
  Purchase #5 $106.87   5.385%   $112.6249   $112.62   $112.60   $112.60  
  Purchase #6 $177.84   9.721%   $195.1278   $195.13   $195.15   $195.10  
  Purchase #7 $28.52   7.735%   $30.726   $30.73   $30.75   $30.70  
  7 purchase totals = $852.93       $913.0770   $913.08   $913.10   $913.00