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	$52.59	11.238%	$58.5001	$58.50	$58.50	$58.50
Purchase #2	$45.28	5.782%	$47.8981	$47.90	$47.90	$47.90
Purchase #3	$88.52	13.499%	$100.4693	$100.47	$100.45	$100.50
Purchase #4	$6.58	10.426%	$7.266	$7.27	$7.25	$7.30
Purchase #5	$68.46	4.642%	$71.6379	$71.64	$71.65	$71.60
Purchase #6	$125.89	8.250%	$136.2759	$136.28	$136.30	$136.30
Purchase #7	$69.53	4.510%	$72.6658	$72.67	$72.65	$72.70
7 purchase totals =	$456.85		$494.7131	$494.73	$494.70	$494.80