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	$237.48	8.322%	$257.2431	$257.24	$257.25	$257.20
Purchase #2	$89.91	7.621%	$96.762	$96.76	$96.75	$96.80
Purchase #3	$177.61	6.717%	$189.5401	$189.54	$189.55	$189.50
Purchase #4	$222.85	10.569%	$246.403	$246.40	$246.40	$246.40
Purchase #5	$91.32	3.457%	$94.4769	$94.48	$94.50	$94.50
Purchase #6	$90.45	4.115%	$94.172	$94.17	$94.15	$94.20
Purchase #7	$37.56	8.831%	$40.8769	$40.88	$40.90	$40.90
7 purchase totals =	$947.18		$1,019.4740	$1,019.47	$1,019.50	$1,019.50