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	$11.44	6.510%	$12.1847	$12.18	$12.20	$12.20
Purchase #2	$182.48	3.859%	$189.5219	$189.52	$189.50	$189.50
Purchase #3	$79.87	11.446%	$89.0119	$89.01	$89.00	$89.00
Purchase #4	$249.89	11.341%	$278.23	$278.23	$278.25	$278.20
Purchase #5	$66.75	7.398%	$71.6882	$71.69	$71.70	$71.70
Purchase #6	$215.89	3.313%	$223.0424	$223.04	$223.05	$223.00
Purchase #7	$126.46	3.641%	$131.0644	$131.06	$131.05	$131.10
7 purchase totals =	$932.78		$994.7435	$994.73	$994.75	$994.70