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 $226.29   8.492%   $245.5065   $245.51   $245.50   $245.50  
  Purchase #2 $182.61   13.584%   $207.4157   $207.42   $207.40   $207.40  
  Purchase #3 $68.82   3.102%   $70.9548   $70.95   $70.95   $71.00  
  Purchase #4 $12.94   12.392%   $14.5435   $14.54   $14.55   $14.50  
  Purchase #5 $77.33   4.128%   $80.5222   $80.52   $80.50   $80.50  
  Purchase #6 $244.85   11.757%   $273.637   $273.64   $273.65   $273.60  
  Purchase #7 $66.76   10.872%   $74.0181   $74.02   $74.00   $74.00  
  7 purchase totals = $879.60       $966.5978   $966.60   $966.55   $966.50