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	$246.60	11.604%	$275.2155	$275.22	$275.20	$275.20
Purchase #2	$33.55	11.141%	$37.2878	$37.29	$37.30	$37.30
Purchase #3	$169.86	7.479%	$182.5638	$182.56	$182.55	$182.60
Purchase #4	$139.97	11.684%	$156.3241	$156.32	$156.30	$156.30
Purchase #5	$104.40	10.506%	$115.3683	$115.37	$115.35	$115.40
Purchase #6	$60.75	8.598%	$65.9733	$65.97	$65.95	$66.00
Purchase #7	$102.82	8.277%	$111.3304	$111.33	$111.35	$111.30
7 purchase totals =	$857.95		$944.0632	$944.06	$944.00	$944.10