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	$243.76	4.155%	$253.8882	$253.89	$253.90	$253.90
Purchase #2	$191.52	10.248%	$211.147	$211.15	$211.15	$211.10
Purchase #3	$27.29	9.417%	$29.8599	$29.86	$29.85	$29.90
Purchase #4	$54.44	9.270%	$59.4866	$59.49	$59.50	$59.50
Purchase #5	$130.52	7.123%	$139.8169	$139.82	$139.80	$139.80
Purchase #6	$166.85	11.485%	$186.0127	$186.01	$186.00	$186.00
Purchase #7	$38.76	6.504%	$41.281	$41.28	$41.30	$41.30
7 purchase totals =	$853.14		$921.4923	$921.50	$921.50	$921.50