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	$210.25	8.820%	$228.7941	$228.79	$228.80	$228.80
Purchase #2	$96.57	9.553%	$105.7953	$105.80	$105.80	$105.80
Purchase #3	$171.42	11.550%	$191.219	$191.22	$191.20	$191.20
Purchase #4	$137.29	10.768%	$152.0734	$152.07	$152.05	$152.10
Purchase #5	$54.66	11.335%	$60.8557	$60.86	$60.85	$60.90
Purchase #6	$74.57	11.595%	$83.2164	$83.22	$83.20	$83.20
Purchase #7	$89.73	13.610%	$101.9423	$101.94	$101.95	$101.90
7 purchase totals =	$834.49		$923.8962	$923.90	$923.85	$923.90