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	$137.64	5.328%	$144.9735	$144.97	$144.95	$145.00
Purchase #2	$156.49	5.592%	$165.2409	$165.24	$165.25	$165.20
Purchase #3	$63.93	13.574%	$72.6079	$72.61	$72.60	$72.60
Purchase #4	$109.38	5.421%	$115.3095	$115.31	$115.30	$115.30
Purchase #5	$57.28	4.542%	$59.8817	$59.88	$59.90	$59.90
Purchase #6	$124.86	11.681%	$139.4449	$139.44	$139.45	$139.40
Purchase #7	$123.83	12.294%	$139.0537	$139.05	$139.05	$139.10
7 purchase totals =	$773.41		$836.5121	$836.50	$836.50	$836.50