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	$113.64	8.256%	$123.0221	$123.02	$123.00	$123.00
Purchase #2	$100.35	12.297%	$112.69	$112.69	$112.70	$112.70
Purchase #3	$86.31	3.779%	$89.5717	$89.57	$89.55	$89.60
Purchase #4	$246.48	8.494%	$267.416	$267.42	$267.40	$267.40
Purchase #5	$56.31	9.167%	$61.4719	$61.47	$61.45	$61.50
Purchase #6	$209.81	6.823%	$224.1253	$224.13	$224.15	$224.10
Purchase #7	$85.27	8.409%	$92.4404	$92.44	$92.45	$92.40
7 purchase totals =	$898.17		$970.7374	$970.74	$970.70	$970.70