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	$99.37	3.613%	$102.9602	$102.96	$102.95	$103.00
Purchase #2	$20.48	3.267%	$21.1491	$21.15	$21.15	$21.10
Purchase #3	$126.74	12.498%	$142.58	$142.58	$142.60	$142.60
Purchase #4	$102.60	11.137%	$114.0266	$114.03	$114.05	$114.00
Purchase #5	$98.88	11.713%	$110.4618	$110.46	$110.45	$110.50
Purchase #6	$61.96	12.605%	$69.7701	$69.77	$69.75	$69.80
Purchase #7	$93.77	6.348%	$99.7225	$99.72	$99.70	$99.70
7 purchase totals =	$603.80		$660.6703	$660.67	$660.65	$660.70