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	$69.49	13.533%	$78.8941	$78.89	$78.90	$78.90
Purchase #2	$162.55	13.524%	$184.5333	$184.53	$184.55	$184.50
Purchase #3	$112.34	13.260%	$127.2363	$127.24	$127.25	$127.20
Purchase #4	$154.72	10.634%	$171.1729	$171.17	$171.15	$171.20
Purchase #5	$116.76	5.427%	$123.0966	$123.10	$123.10	$123.10
Purchase #6	$54.90	9.339%	$60.0271	$60.03	$60.05	$60.00
Purchase #7	$57.59	10.223%	$63.4774	$63.48	$63.50	$63.50
7 purchase totals =	$728.35		$808.4377	$808.44	$808.50	$808.40