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	$169.67	11.630%	$189.4026	$189.40	$189.40	$189.40
Purchase #2	$62.71	13.723%	$71.3157	$71.32	$71.30	$71.30
Purchase #3	$138.29	8.573%	$150.1456	$150.15	$150.15	$150.10
Purchase #4	$82.92	4.645%	$86.7716	$86.77	$86.75	$86.80
Purchase #5	$46.82	13.162%	$52.9824	$52.98	$53.00	$53.00
Purchase #6	$7.53	8.424%	$8.1643	$8.16	$8.15	$8.20
Purchase #7	$235.45	13.874%	$268.1163	$268.12	$268.10	$268.10
7 purchase totals =	$743.39		$826.8985	$826.90	$826.85	$826.90