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	$180.73	5.811%	$191.2322	$191.23	$191.25	$191.20
Purchase #2	$48.69	10.804%	$53.9505	$53.95	$53.95	$54.00
Purchase #3	$107.32	6.227%	$114.0028	$114.00	$114.00	$114.00
Purchase #4	$92.42	3.674%	$95.8155	$95.82	$95.80	$95.80
Purchase #5	$139.27	11.728%	$155.6036	$155.60	$155.60	$155.60
Purchase #6	$201.93	12.366%	$226.9007	$226.90	$226.90	$226.90
Purchase #7	$159.72	3.310%	$165.0067	$165.01	$165.00	$165.00
7 purchase totals =	$930.08		$1,002.5120	$1,002.51	$1,002.50	$1,002.50