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	$92.94	4.854%	$97.4513	$97.45	$97.45	$97.50
Purchase #2	$220.63	3.872%	$229.1728	$229.17	$229.15	$229.20
Purchase #3	$171.53	4.660%	$179.5233	$179.52	$179.50	$179.50
Purchase #4	$149.48	11.874%	$167.2293	$167.23	$167.25	$167.20
Purchase #5	$37.71	12.530%	$42.4351	$42.44	$42.45	$42.40
Purchase #6	$84.71	6.552%	$90.2602	$90.26	$90.25	$90.30
Purchase #7	$169.81	13.713%	$193.096	$193.10	$193.10	$193.10
7 purchase totals =	$926.81		$999.1680	$999.17	$999.15	$999.20