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	$90.83	9.410%	$99.3771	$99.38	$99.40	$99.40
Purchase #2	$222.67	11.173%	$247.5489	$247.55	$247.55	$247.50
Purchase #3	$47.61	5.352%	$50.1581	$50.16	$50.15	$50.20
Purchase #4	$131.36	7.802%	$141.6087	$141.61	$141.60	$141.60
Purchase #5	$79.84	8.842%	$86.8995	$86.90	$86.90	$86.90
Purchase #6	$28.90	5.127%	$30.3817	$30.38	$30.40	$30.40
Purchase #7	$65.58	3.248%	$67.71	$67.71	$67.70	$67.70
7 purchase totals =	$666.79		$723.6840	$723.69	$723.70	$723.70