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	$79.91	3.552%	$82.7484	$82.75	$82.75	$82.70
Purchase #2	$162.38	3.391%	$167.8863	$167.89	$167.90	$167.90
Purchase #3	$89.55	9.803%	$98.3286	$98.33	$98.35	$98.30
Purchase #4	$231.90	8.182%	$250.8741	$250.87	$250.85	$250.90
Purchase #5	$130.82	5.447%	$137.9458	$137.95	$137.95	$137.90
Purchase #6	$116.40	12.593%	$131.0583	$131.06	$131.05	$131.10
Purchase #7	$236.75	9.657%	$259.6129	$259.61	$259.60	$259.60
7 purchase totals =	$1,047.71		$1,128.4544	$1,128.46	$1,128.45	$1,128.40