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	$250.57	8.322%	$271.4224	$271.42	$271.40	$271.40
Purchase #2	$126.32	10.514%	$139.6013	$139.60	$139.60	$139.60
Purchase #3	$209.90	8.809%	$228.3901	$228.39	$228.40	$228.40
Purchase #4	$226.82	9.143%	$247.5582	$247.56	$247.55	$247.60
Purchase #5	$189.94	12.639%	$213.9465	$213.95	$213.95	$213.90
Purchase #6	$178.43	10.107%	$196.4639	$196.46	$196.45	$196.50
Purchase #7	$49.91	12.223%	$56.0105	$56.01	$56.00	$56.00
7 purchase totals =	$1,231.89		$1,353.3929	$1,353.39	$1,353.35	$1,353.40