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	$220.64	5.742%	$233.3091	$233.31	$233.30	$233.30
Purchase #2	$85.37	6.493%	$90.9131	$90.91	$90.90	$90.90
Purchase #3	$231.50	5.365%	$243.92	$243.92	$243.90	$243.90
Purchase #4	$109.88	7.494%	$118.1144	$118.11	$118.10	$118.10
Purchase #5	$52.65	9.603%	$57.706	$57.71	$57.70	$57.70
Purchase #6	$201.50	8.517%	$218.6618	$218.66	$218.65	$218.70
Purchase #7	$73.34	4.409%	$76.5736	$76.57	$76.55	$76.60
7 purchase totals =	$974.88		$1,039.1980	$1,039.19	$1,039.10	$1,039.20