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	$151.25	13.362%	$171.46	$171.46	$171.45	$171.50
Purchase #2	$172.49	7.690%	$185.7545	$185.75	$185.75	$185.80
Purchase #3	$57.30	11.391%	$63.827	$63.83	$63.85	$63.80
Purchase #4	$238.76	9.465%	$261.3586	$261.36	$261.35	$261.40
Purchase #5	$211.31	3.121%	$217.905	$217.91	$217.90	$217.90
Purchase #6	$128.68	8.361%	$139.4389	$139.44	$139.45	$139.40
Purchase #7	$93.54	5.265%	$98.4649	$98.46	$98.45	$98.50
7 purchase totals =	$1,053.33		$1,138.2089	$1,138.21	$1,138.20	$1,138.30