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	$88.67	11.650%	$99.0001	$99.00	$99.00	$99.00
Purchase #2	$54.37	13.184%	$61.5381	$61.54	$61.55	$61.50
Purchase #3	$28.50	6.549%	$30.3665	$30.37	$30.35	$30.40
Purchase #4	$210.26	7.441%	$225.9054	$225.91	$225.90	$225.90
Purchase #5	$153.74	11.531%	$171.4678	$171.47	$171.45	$171.50
Purchase #6	$174.45	4.418%	$182.1572	$182.16	$182.15	$182.20
Purchase #7	$127.66	11.238%	$142.0064	$142.01	$142.00	$142.00
7 purchase totals =	$837.65		$912.4415	$912.46	$912.40	$912.50