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	$29.56	7.691%	$31.8335	$31.83	$31.85	$31.80
Purchase #2	$225.55	5.569%	$238.1109	$238.11	$238.10	$238.10
Purchase #3	$96.69	10.741%	$107.0755	$107.08	$107.10	$107.10
Purchase #4	$83.53	6.754%	$89.1716	$89.17	$89.15	$89.20
Purchase #5	$88.31	11.385%	$98.3641	$98.36	$98.35	$98.40
Purchase #6	$96.55	3.255%	$99.6927	$99.69	$99.70	$99.70
Purchase #7	$244.78	9.513%	$268.0659	$268.07	$268.05	$268.10
7 purchase totals =	$864.97		$932.3142	$932.31	$932.30	$932.40