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	$46.26	12.111%	$51.8625	$51.86	$51.85	$51.90
Purchase #2	$56.97	8.674%	$61.9116	$61.91	$61.90	$61.90
Purchase #3	$124.53	9.779%	$136.7078	$136.71	$136.70	$136.70
Purchase #4	$182.72	7.499%	$196.4222	$196.42	$196.40	$196.40
Purchase #5	$219.88	12.726%	$247.8619	$247.86	$247.85	$247.90
Purchase #6	$78.86	9.407%	$86.2784	$86.28	$86.30	$86.30
Purchase #7	$207.42	6.545%	$220.9956	$221.00	$221.00	$221.00
7 purchase totals =	$916.64		$1,002.0400	$1,002.04	$1,002.00	$1,002.10