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	$77.66	4.220%	$80.9373	$80.94	$80.95	$80.90
Purchase #2	$196.79	9.469%	$215.424	$215.42	$215.40	$215.40
Purchase #3	$215.40	12.768%	$242.9023	$242.90	$242.90	$242.90
Purchase #4	$216.89	13.151%	$245.4132	$245.41	$245.40	$245.40
Purchase #5	$18.25	10.740%	$20.2101	$20.21	$20.20	$20.20
Purchase #6	$128.81	13.746%	$146.5162	$146.52	$146.50	$146.50
Purchase #7	$70.82	12.713%	$79.8233	$79.82	$79.80	$79.80
7 purchase totals =	$924.62		$1,031.2264	$1,031.22	$1,031.15	$1,031.10