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	$249.82	12.135%	$280.1357	$280.14	$280.15	$280.10
Purchase #2	$221.45	12.680%	$249.5299	$249.53	$249.55	$249.50
Purchase #3	$171.86	7.707%	$185.1053	$185.11	$185.10	$185.10
Purchase #4	$54.81	8.539%	$59.4902	$59.49	$59.50	$59.50
Purchase #5	$53.83	11.842%	$60.2045	$60.20	$60.20	$60.20
Purchase #6	$181.73	10.298%	$200.4446	$200.44	$200.45	$200.40
Purchase #7	$28.84	9.673%	$31.6297	$31.63	$31.65	$31.60
7 purchase totals =	$962.34		$1,066.5399	$1,066.54	$1,066.60	$1,066.40