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	$247.79	11.269%	$275.7135	$275.71	$275.70	$275.70
Purchase #2	$79.36	12.526%	$89.3006	$89.30	$89.30	$89.30
Purchase #3	$205.40	11.124%	$228.2487	$228.25	$228.25	$228.20
Purchase #4	$5.34	13.437%	$6.0575	$6.06	$6.05	$6.10
Purchase #5	$7.89	7.352%	$8.4701	$8.47	$8.45	$8.50
Purchase #6	$70.83	12.145%	$79.4323	$79.43	$79.45	$79.40
Purchase #7	$89.76	8.410%	$97.3088	$97.31	$97.30	$97.30
7 purchase totals =	$706.37		$784.5315	$784.53	$784.50	$784.50