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	$133.56	4.238%	$139.2203	$139.22	$139.20	$139.20
Purchase #2	$42.37	11.388%	$47.1951	$47.20	$47.20	$47.20
Purchase #3	$171.38	8.169%	$185.38	$185.38	$185.40	$185.40
Purchase #4	$239.81	6.641%	$255.7358	$255.74	$255.75	$255.70
Purchase #5	$84.75	11.478%	$94.4776	$94.48	$94.50	$94.50
Purchase #6	$28.81	12.193%	$32.3228	$32.32	$32.30	$32.30
Purchase #7	$35.74	8.667%	$38.8376	$38.84	$38.85	$38.80
7 purchase totals =	$736.42		$793.1692	$793.18	$793.20	$793.10