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	$232.34	13.625%	$263.9963	$264.00	$264.00	$264.00
Purchase #2	$122.65	6.792%	$130.9804	$130.98	$131.00	$131.00
Purchase #3	$136.26	4.215%	$142.0034	$142.00	$142.00	$142.00
Purchase #4	$132.34	13.740%	$150.5235	$150.52	$150.50	$150.50
Purchase #5	$217.77	12.793%	$245.6293	$245.63	$245.65	$245.60
Purchase #6	$104.46	11.737%	$116.7205	$116.72	$116.70	$116.70
Purchase #7	$79.44	12.844%	$89.6433	$89.64	$89.65	$89.60
7 purchase totals =	$1,025.26		$1,139.4967	$1,139.49	$1,139.50	$1,139.40