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	$242.44	6.267%	$257.6337	$257.63	$257.65	$257.60
Purchase #2	$96.67	8.870%	$105.2446	$105.24	$105.25	$105.20
Purchase #3	$236.99	7.307%	$254.3069	$254.31	$254.30	$254.30
Purchase #4	$37.72	8.110%	$40.7791	$40.78	$40.80	$40.80
Purchase #5	$59.46	9.818%	$65.2978	$65.30	$65.30	$65.30
Purchase #6	$104.71	5.347%	$110.3088	$110.31	$110.30	$110.30
Purchase #7	$157.92	8.567%	$171.449	$171.45	$171.45	$171.40
7 purchase totals =	$935.91		$1,005.0199	$1,005.02	$1,005.05	$1,004.90