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	$82.72	10.326%	$91.2617	$91.26	$91.25	$91.30
Purchase #2	$249.89	10.602%	$276.3833	$276.38	$276.40	$276.40
Purchase #3	$65.38	5.144%	$68.7431	$68.74	$68.75	$68.70
Purchase #4	$115.43	13.131%	$130.5871	$130.59	$130.60	$130.60
Purchase #5	$116.79	12.221%	$131.0629	$131.06	$131.05	$131.10
Purchase #6	$229.37	6.313%	$243.8501	$243.85	$243.85	$243.90
Purchase #7	$56.44	8.811%	$61.4129	$61.41	$61.40	$61.40
7 purchase totals =	$916.02		$1,003.3011	$1,003.29	$1,003.30	$1,003.40