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 $112.47   10.848%   $124.6707   $124.67   $124.65   $124.70  
  Purchase #2 $188.36   8.179%   $203.766   $203.77   $203.75   $203.80  
  Purchase #3 $32.90   6.634%   $35.0826   $35.08   $35.10   $35.10  
  Purchase #4 $185.52   13.816%   $211.1514   $211.15   $211.15   $211.20  
  Purchase #5 $136.93   6.496%   $145.825   $145.83   $145.85   $145.80  
  Purchase #6 $30.50   6.869%   $32.595   $32.60   $32.60   $32.60  
  Purchase #7 $21.54   6.510%   $22.9423   $22.94   $22.95   $22.90  
  7 purchase totals = $708.22       $776.0330   $776.04   $776.05   $776.10