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	$64.97	11.662%	$72.5468	$72.55	$72.55	$72.50
Purchase #2	$250.27	10.297%	$276.0403	$276.04	$276.05	$276.00
Purchase #3	$139.97	12.738%	$157.7994	$157.80	$157.80	$157.80
Purchase #4	$59.75	10.319%	$65.9156	$65.92	$65.90	$65.90
Purchase #5	$57.49	10.467%	$63.5075	$63.51	$63.50	$63.50
Purchase #6	$110.50	9.218%	$120.6859	$120.69	$120.70	$120.70
Purchase #7	$82.85	8.411%	$89.8185	$89.82	$89.80	$89.80
7 purchase totals =	$765.80		$846.3140	$846.33	$846.30	$846.20