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	$140.69	4.459%	$146.9634	$146.96	$146.95	$147.00
Purchase #2	$123.62	12.775%	$139.4125	$139.41	$139.40	$139.40
Purchase #3	$249.69	10.206%	$275.1734	$275.17	$275.15	$275.20
Purchase #4	$106.66	4.571%	$111.5354	$111.54	$111.55	$111.50
Purchase #5	$61.90	10.719%	$68.5351	$68.54	$68.55	$68.50
Purchase #6	$166.33	6.810%	$177.6571	$177.66	$177.65	$177.70
Purchase #7	$75.92	3.754%	$78.77	$78.77	$78.75	$78.80
7 purchase totals =	$924.81		$998.0469	$998.05	$998.00	$998.10