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	$106.90	6.432%	$113.7758	$113.78	$113.80	$113.80
Purchase #2	$210.57	7.286%	$225.9121	$225.91	$225.90	$225.90
Purchase #3	$27.81	13.215%	$31.4851	$31.49	$31.50	$31.50
Purchase #4	$137.74	5.187%	$144.8846	$144.88	$144.90	$144.90
Purchase #5	$172.32	6.839%	$184.105	$184.11	$184.10	$184.10
Purchase #6	$84.44	4.380%	$88.1385	$88.14	$88.15	$88.10
Purchase #7	$42.41	9.708%	$46.5272	$46.53	$46.55	$46.50
7 purchase totals =	$782.19		$834.8283	$834.84	$834.90	$834.80