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	$78.97	13.275%	$89.4533	$89.45	$89.45	$89.50
Purchase #2	$167.91	13.405%	$190.4183	$190.42	$190.40	$190.40
Purchase #3	$89.64	9.820%	$98.4426	$98.44	$98.45	$98.40
Purchase #4	$177.33	3.160%	$182.9336	$182.93	$182.95	$182.90
Purchase #5	$165.33	3.684%	$171.4208	$171.42	$171.40	$171.40
Purchase #6	$26.81	9.275%	$29.2966	$29.30	$29.30	$29.30
Purchase #7	$42.39	8.705%	$46.08	$46.08	$46.10	$46.10
7 purchase totals =	$748.38		$808.0452	$808.04	$808.05	$808.00