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 $64.52   13.517%   $73.2412   $73.24   $73.25   $73.20  
  Purchase #2 $86.86   11.156%   $96.5501   $96.55   $96.55   $96.60  
  Purchase #3 $86.78   7.795%   $93.5445   $93.54   $93.55   $93.50  
  Purchase #4 $195.64   6.585%   $208.5229   $208.52   $208.50   $208.50  
  Purchase #5 $213.36   10.135%   $234.984   $234.98   $235.00   $235.00  
  Purchase #6 $121.43   10.208%   $133.8256   $133.83   $133.85   $133.80  
  Purchase #7 $22.79   4.574%   $23.8324   $23.83   $23.85   $23.80  
  7 purchase totals = $791.38       $864.5007   $864.49   $864.55   $864.40