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 $52.81   6.331%   $56.1534   $56.15   $56.15   $56.20  
  Purchase #2 $174.32   13.191%   $197.3146   $197.31   $197.30   $197.30  
  Purchase #3 $73.96   11.710%   $82.6207   $82.62   $82.60   $82.60  
  Purchase #4 $17.63   4.355%   $18.3978   $18.40   $18.40   $18.40  
  Purchase #5 $228.47   3.767%   $237.0765   $237.08   $237.10   $237.10  
  Purchase #6 $148.78   10.775%   $164.811   $164.81   $164.80   $164.80  
  Purchase #7 $17.51   12.141%   $19.6359   $19.64   $19.65   $19.60  
  7 purchase totals = $713.48       $776.0099   $776.01   $776.00   $776.00