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 $59.55   3.267%   $61.4955   $61.50   $61.50   $61.50  
  Purchase #2 $158.83   11.413%   $176.9573   $176.96   $176.95   $177.00  
  Purchase #3 $186.69   13.579%   $212.0406   $212.04   $212.05   $212.00  
  Purchase #4 $222.64   3.330%   $230.0539   $230.05   $230.05   $230.10  
  Purchase #5 $168.60   8.346%   $182.6714   $182.67   $182.65   $182.70  
  Purchase #6 $120.26   12.631%   $135.45   $135.45   $135.45   $135.50  
  Purchase #7 $170.93   11.187%   $190.0519   $190.05   $190.05   $190.10  
  7 purchase totals = $1,087.50       $1,188.7206   $1,188.72   $1,188.70   $1,188.90