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	$40.46	12.221%	$45.4046	$45.40	$45.40	$45.40
Purchase #2	$228.59	8.623%	$248.3013	$248.30	$248.30	$248.30
Purchase #3	$228.53	7.102%	$244.7602	$244.76	$244.75	$244.80
Purchase #4	$191.44	10.460%	$211.4646	$211.46	$211.45	$211.50
Purchase #5	$72.64	7.506%	$78.0924	$78.09	$78.10	$78.10
Purchase #6	$240.31	9.705%	$263.6321	$263.63	$263.65	$263.60
Purchase #7	$46.71	9.375%	$51.0891	$51.09	$51.10	$51.10
7 purchase totals =	$1,048.68		$1,142.7443	$1,142.73	$1,142.75	$1,142.80