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 $85.72   12.282%   $96.2481   $96.25   $96.25   $96.20  
  Purchase #2 $23.78   11.806%   $26.5875   $26.59   $26.60   $26.60  
  Purchase #3 $127.83   10.403%   $141.1282   $141.13   $141.15   $141.10  
  Purchase #4 $46.47   4.836%   $48.7173   $48.72   $48.70   $48.70  
  Purchase #5 $249.93   11.422%   $278.477   $278.48   $278.50   $278.50  
  Purchase #6 $34.65   12.554%   $39   $39.00   $39.00   $39.00  
  Purchase #7 $177.52   11.573%   $198.0644   $198.06   $198.05   $198.10  
  7 purchase totals = $745.90       $828.2225   $828.23   $828.25   $828.20