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	$45.46	3.156%	$46.8947	$46.89	$46.90	$46.90
Purchase #2	$101.85	12.156%	$114.2309	$114.23	$114.25	$114.20
Purchase #3	$168.38	11.792%	$188.2354	$188.24	$188.25	$188.20
Purchase #4	$102.53	7.592%	$110.3141	$110.31	$110.30	$110.30
Purchase #5	$139.84	11.474%	$155.8852	$155.89	$155.90	$155.90
Purchase #6	$50.73	13.607%	$57.6328	$57.63	$57.65	$57.60
Purchase #7	$39.30	13.104%	$44.4499	$44.45	$44.45	$44.40
7 purchase totals =	$648.09		$717.6430	$717.64	$717.70	$717.50