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 $46.81   13.848%   $53.2922   $53.29   $53.30   $53.30  
  Purchase #2 $246.94   10.863%   $273.7651   $273.77   $273.75   $273.80  
  Purchase #3 $142.80   4.554%   $149.3031   $149.30   $149.30   $149.30  
  Purchase #4 $22.97   6.520%   $24.4676   $24.47   $24.45   $24.50  
  Purchase #5 $224.52   5.690%   $237.2952   $237.30   $237.30   $237.30  
  Purchase #6 $65.51   9.480%   $71.7203   $71.72   $71.70   $71.70  
  Purchase #7 $174.39   6.778%   $186.2102   $186.21   $186.20   $186.20  
  7 purchase totals = $923.94       $996.0537   $996.06   $996.00   $996.10