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	$245.90	11.330%	$273.7605	$273.76	$273.75	$273.80
Purchase #2	$42.89	12.819%	$48.3881	$48.39	$48.40	$48.40
Purchase #3	$236.48	8.852%	$257.4132	$257.41	$257.40	$257.40
Purchase #4	$171.78	10.753%	$190.2515	$190.25	$190.25	$190.30
Purchase #5	$123.93	11.276%	$137.9043	$137.90	$137.90	$137.90
Purchase #6	$190.61	4.289%	$198.7853	$198.79	$198.80	$198.80
Purchase #7	$145.92	4.501%	$152.4879	$152.49	$152.50	$152.50
7 purchase totals =	$1,157.51		$1,258.9908	$1,258.99	$1,259.00	$1,259.10