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	$143.37	4.844%	$150.3148	$150.31	$150.30	$150.30
Purchase #2	$92.77	8.369%	$100.5339	$100.53	$100.55	$100.50
Purchase #3	$210.71	12.163%	$236.3387	$236.34	$236.35	$236.30
Purchase #4	$96.71	13.404%	$109.673	$109.67	$109.65	$109.70
Purchase #5	$165.44	4.822%	$173.4175	$173.42	$173.40	$173.40
Purchase #6	$196.41	13.559%	$223.0412	$223.04	$223.05	$223.00
Purchase #7	$238.80	3.320%	$246.7282	$246.73	$246.75	$246.70
7 purchase totals =	$1,144.21		$1,240.0473	$1,240.04	$1,240.05	$1,239.90