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	$29.42	5.765%	$31.1161	$31.12	$31.10	$31.10
Purchase #2	$186.63	9.577%	$204.5036	$204.50	$204.50	$204.50
Purchase #3	$81.69	12.123%	$91.5933	$91.59	$91.60	$91.60
Purchase #4	$132.33	5.734%	$139.9178	$139.92	$139.90	$139.90
Purchase #5	$218.78	4.597%	$228.8373	$228.84	$228.85	$228.80
Purchase #6	$79.72	11.144%	$88.604	$88.60	$88.60	$88.60
Purchase #7	$159.72	12.285%	$179.3416	$179.34	$179.35	$179.30
7 purchase totals =	$888.29		$963.9137	$963.91	$963.90	$963.80