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 $235.64   10.863%   $261.2376   $261.24   $261.25   $261.20  
  Purchase #2 $68.94   9.435%   $75.4445   $75.44   $75.45   $75.40  
  Purchase #3 $182.47   8.322%   $197.6552   $197.66   $197.65   $197.70  
  Purchase #4 $42.27   5.328%   $44.5221   $44.52   $44.50   $44.50  
  Purchase #5 $23.31   12.864%   $26.3086   $26.31   $26.30   $26.30  
  Purchase #6 $56.51   12.819%   $63.754   $63.75   $63.75   $63.80  
  Purchase #7 $213.39   10.600%   $236.0093   $236.01   $236.00   $236.00  
  7 purchase totals = $822.53       $904.9313   $904.93   $904.90   $904.90