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 $216.47   8.674%   $235.2466   $235.25   $235.25   $235.20  
  Purchase #2 $77.34   6.499%   $82.3663   $82.37   $82.35   $82.40  
  Purchase #3 $240.39   3.512%   $248.8325   $248.83   $248.85   $248.80  
  Purchase #4 $9.73   9.555%   $10.6597   $10.66   $10.65   $10.70  
  Purchase #5 $200.88   3.837%   $208.5878   $208.59   $208.60   $208.60  
  Purchase #6 $178.52   7.338%   $191.6198   $191.62   $191.60   $191.60  
  Purchase #7 $72.99   5.349%   $76.8942   $76.89   $76.90   $76.90  
  7 purchase totals = $996.32       $1,054.2069   $1,054.21   $1,054.20   $1,054.20