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	$41.53	9.818%	$45.6074	$45.61	$45.60	$45.60
Purchase #2	$20.80	6.681%	$22.1896	$22.19	$22.20	$22.20
Purchase #3	$72.48	7.705%	$78.0646	$78.06	$78.05	$78.10
Purchase #4	$57.67	9.180%	$62.9641	$62.96	$62.95	$63.00
Purchase #5	$85.82	4.118%	$89.3541	$89.35	$89.35	$89.40
Purchase #6	$98.69	10.115%	$108.6725	$108.67	$108.65	$108.70
Purchase #7	$228.74	12.374%	$257.0443	$257.04	$257.05	$257.00
7 purchase totals =	$605.73		$663.8966	$663.88	$663.85	$664.00