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	$67.77	8.526%	$73.5481	$73.55	$73.55	$73.50
Purchase #2	$192.35	13.532%	$218.3788	$218.38	$218.40	$218.40
Purchase #3	$170.46	10.126%	$187.7208	$187.72	$187.70	$187.70
Purchase #4	$181.62	7.278%	$194.8383	$194.84	$194.85	$194.80
Purchase #5	$171.34	11.337%	$190.7648	$190.76	$190.75	$190.80
Purchase #6	$65.39	9.445%	$71.5661	$71.57	$71.55	$71.60
Purchase #7	$82.30	3.368%	$85.0719	$85.07	$85.05	$85.10
7 purchase totals =	$931.23		$1,021.8888	$1,021.89	$1,021.85	$1,021.90