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	$248.88	8.134%	$269.1239	$269.12	$269.10	$269.10
Purchase #2	$189.77	10.665%	$210.009	$210.01	$210.00	$210.00
Purchase #3	$69.67	12.577%	$78.4324	$78.43	$78.45	$78.40
Purchase #4	$71.86	7.183%	$77.0217	$77.02	$77.00	$77.00
Purchase #5	$45.62	11.274%	$50.7632	$50.76	$50.75	$50.80
Purchase #6	$71.76	12.189%	$80.5068	$80.51	$80.50	$80.50
Purchase #7	$56.50	8.686%	$61.4076	$61.41	$61.40	$61.40
7 purchase totals =	$754.06		$827.2646	$827.26	$827.20	$827.20