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	$135.50	10.329%	$149.4958	$149.50	$149.50	$149.50
Purchase #2	$56.92	3.777%	$59.0699	$59.07	$59.05	$59.10
Purchase #3	$22.59	11.635%	$25.2183	$25.22	$25.20	$25.20
Purchase #4	$147.80	12.210%	$165.8464	$165.85	$165.85	$165.80
Purchase #5	$194.32	7.763%	$209.4051	$209.41	$209.40	$209.40
Purchase #6	$55.56	11.557%	$61.9811	$61.98	$62.00	$62.00
Purchase #7	$225.90	7.609%	$243.0887	$243.09	$243.10	$243.10
7 purchase totals =	$838.59		$914.1053	$914.12	$914.10	$914.10