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	$74.36	10.264%	$81.9923	$81.99	$82.00	$82.00
Purchase #2	$79.32	3.727%	$82.2763	$82.28	$82.30	$82.30
Purchase #3	$91.56	12.512%	$103.016	$103.02	$103.00	$103.00
Purchase #4	$185.68	6.695%	$198.1113	$198.11	$198.10	$198.10
Purchase #5	$144.84	10.304%	$159.7643	$159.76	$159.75	$159.80
Purchase #6	$158.96	7.485%	$170.8582	$170.86	$170.85	$170.90
Purchase #7	$41.71	3.836%	$43.31	$43.31	$43.30	$43.30
7 purchase totals =	$776.43		$839.3284	$839.33	$839.30	$839.40