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	$9.72	12.331%	$10.9186	$10.92	$10.90	$10.90
Purchase #2	$188.39	9.329%	$205.9649	$205.96	$205.95	$206.00
Purchase #3	$135.33	5.220%	$142.3942	$142.39	$142.40	$142.40
Purchase #4	$72.45	6.303%	$77.0165	$77.02	$77.00	$77.00
Purchase #5	$233.59	7.278%	$250.5907	$250.59	$250.60	$250.60
Purchase #6	$26.48	4.561%	$27.6878	$27.69	$27.70	$27.70
Purchase #7	$140.26	7.168%	$150.3138	$150.31	$150.30	$150.30
7 purchase totals =	$806.22		$864.8865	$864.88	$864.85	$864.90