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	$180.89	4.611%	$189.2308	$189.23	$189.25	$189.20
Purchase #2	$55.83	9.838%	$61.3226	$61.32	$61.30	$61.30
Purchase #3	$122.63	6.442%	$130.5298	$130.53	$130.55	$130.50
Purchase #4	$74.25	11.447%	$82.7494	$82.75	$82.75	$82.70
Purchase #5	$31.41	13.306%	$35.5894	$35.59	$35.60	$35.60
Purchase #6	$67.59	11.560%	$75.4034	$75.40	$75.40	$75.40
Purchase #7	$23.73	13.204%	$26.8633	$26.86	$26.85	$26.90
7 purchase totals =	$556.33		$601.6887	$601.68	$601.70	$601.60