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	$173.88	6.200%	$184.6606	$184.66	$184.65	$184.70
Purchase #2	$159.41	9.373%	$174.3515	$174.35	$174.35	$174.40
Purchase #3	$152.69	11.688%	$170.5364	$170.54	$170.55	$170.50
Purchase #4	$154.82	6.437%	$164.7858	$164.79	$164.80	$164.80
Purchase #5	$239.79	10.510%	$264.9919	$264.99	$265.00	$265.00
Purchase #6	$79.42	11.159%	$88.2825	$88.28	$88.30	$88.30
Purchase #7	$91.50	9.109%	$99.8347	$99.83	$99.85	$99.80
7 purchase totals =	$1,051.51		$1,147.4434	$1,147.44	$1,147.50	$1,147.50