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	$110.91	6.637%	$118.2711	$118.27	$118.25	$118.30
Purchase #2	$221.83	10.227%	$244.5166	$244.52	$244.50	$244.50
Purchase #3	$198.33	13.586%	$225.2751	$225.28	$225.30	$225.30
Purchase #4	$179.84	11.663%	$200.8147	$200.81	$200.80	$200.80
Purchase #5	$55.46	7.479%	$59.6079	$59.61	$59.60	$59.60
Purchase #6	$162.78	9.698%	$178.5664	$178.57	$178.55	$178.60
Purchase #7	$243.85	8.660%	$264.9674	$264.97	$264.95	$265.00
7 purchase totals =	$1,173.00		$1,292.0192	$1,292.03	$1,291.95	$1,292.10