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	$11.33	10.287%	$12.4955	$12.50	$12.50	$12.50
Purchase #2	$223.42	6.656%	$238.2908	$238.29	$238.30	$238.30
Purchase #3	$247.48	7.214%	$265.3332	$265.33	$265.35	$265.30
Purchase #4	$139.71	11.501%	$155.778	$155.78	$155.80	$155.80
Purchase #5	$142.79	5.696%	$150.9233	$150.92	$150.90	$150.90
Purchase #6	$191.89	12.441%	$215.763	$215.76	$215.75	$215.80
Purchase #7	$29.31	6.144%	$31.1108	$31.11	$31.10	$31.10
7 purchase totals =	$985.93		$1,069.6946	$1,069.69	$1,069.70	$1,069.70