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	$33.72	10.718%	$37.3341	$37.33	$37.35	$37.30
Purchase #2	$169.92	11.502%	$189.4642	$189.46	$189.45	$189.50
Purchase #3	$116.78	10.726%	$129.3058	$129.31	$129.30	$129.30
Purchase #4	$59.61	13.871%	$67.8785	$67.88	$67.90	$67.90
Purchase #5	$157.41	13.266%	$178.292	$178.29	$178.30	$178.30
Purchase #6	$40.71	5.724%	$43.0402	$43.04	$43.05	$43.00
Purchase #7	$8.35	13.465%	$9.4743	$9.47	$9.45	$9.50
7 purchase totals =	$586.50		$654.7891	$654.78	$654.80	$654.80