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	$79.50	11.857%	$88.9263	$88.93	$88.95	$88.90
Purchase #2	$80.26	6.524%	$85.4962	$85.50	$85.50	$85.50
Purchase #3	$85.57	8.505%	$92.8477	$92.85	$92.85	$92.80
Purchase #4	$106.85	4.221%	$111.3601	$111.36	$111.35	$111.40
Purchase #5	$77.82	10.646%	$86.1047	$86.10	$86.10	$86.10
Purchase #6	$88.66	6.790%	$94.68	$94.68	$94.70	$94.70
Purchase #7	$101.96	6.449%	$108.5354	$108.54	$108.55	$108.50
7 purchase totals =	$620.62		$667.9504	$667.96	$668.00	$667.90