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	$25.67	10.289%	$28.3112	$28.31	$28.30	$28.30
Purchase #2	$168.44	12.865%	$190.1098	$190.11	$190.10	$190.10
Purchase #3	$54.62	3.529%	$56.5475	$56.55	$56.55	$56.50
Purchase #4	$80.56	12.119%	$90.3231	$90.32	$90.30	$90.30
Purchase #5	$182.55	7.613%	$196.4475	$196.45	$196.45	$196.40
Purchase #6	$89.63	8.317%	$97.0845	$97.08	$97.10	$97.10
Purchase #7	$71.72	13.745%	$81.5779	$81.58	$81.60	$81.60
7 purchase totals =	$673.19		$740.4015	$740.40	$740.40	$740.30