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	$98.68	5.782%	$104.3857	$104.39	$104.40	$104.40
Purchase #2	$85.82	9.523%	$93.9926	$93.99	$94.00	$94.00
Purchase #3	$85.86	5.179%	$90.3067	$90.31	$90.30	$90.30
Purchase #4	$88.25	6.571%	$94.0489	$94.05	$94.05	$94.00
Purchase #5	$136.73	13.636%	$155.3745	$155.37	$155.35	$155.40
Purchase #6	$144.70	5.258%	$152.3083	$152.31	$152.30	$152.30
Purchase #7	$56.73	5.317%	$59.7463	$59.75	$59.75	$59.70
7 purchase totals =	$696.77		$750.1630	$750.17	$750.15	$750.10