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	$11.70	7.182%	$12.5403	$12.54	$12.55	$12.50
Purchase #2	$246.61	10.844%	$273.3524	$273.35	$273.35	$273.40
Purchase #3	$141.40	6.209%	$150.1795	$150.18	$150.20	$150.20
Purchase #4	$165.78	8.507%	$179.8829	$179.88	$179.90	$179.90
Purchase #5	$101.94	12.746%	$114.9333	$114.93	$114.95	$114.90
Purchase #6	$16.52	13.474%	$18.7459	$18.75	$18.75	$18.70
Purchase #7	$37.56	12.412%	$42.2219	$42.22	$42.20	$42.20
7 purchase totals =	$721.51		$791.8562	$791.85	$791.90	$791.80