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	$25.47	12.115%	$28.5557	$28.56	$28.55	$28.60
Purchase #2	$85.73	4.352%	$89.461	$89.46	$89.45	$89.50
Purchase #3	$18.72	7.449%	$20.1145	$20.11	$20.10	$20.10
Purchase #4	$216.29	8.155%	$233.9284	$233.93	$233.95	$233.90
Purchase #5	$86.86	9.846%	$95.4122	$95.41	$95.40	$95.40
Purchase #6	$216.96	7.339%	$232.8827	$232.88	$232.90	$232.90
Purchase #7	$205.35	10.612%	$227.1417	$227.14	$227.15	$227.10
7 purchase totals =	$855.38		$927.4962	$927.49	$927.50	$927.50