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	$75.55	4.433%	$78.8991	$78.90	$78.90	$78.90
Purchase #2	$188.57	13.366%	$213.7743	$213.77	$213.75	$213.80
Purchase #3	$66.37	5.384%	$69.9434	$69.94	$69.95	$69.90
Purchase #4	$89.36	11.817%	$99.9197	$99.92	$99.90	$99.90
Purchase #5	$214.71	9.562%	$235.2406	$235.24	$235.25	$235.20
Purchase #6	$91.64	13.810%	$104.2955	$104.30	$104.30	$104.30
Purchase #7	$168.89	13.709%	$192.0431	$192.04	$192.05	$192.00
7 purchase totals =	$895.09		$994.1157	$994.11	$994.10	$994.00