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	$25.82	8.628%	$28.0477	$28.05	$28.05	$28.00
Purchase #2	$99.77	4.392%	$104.1519	$104.15	$104.15	$104.20
Purchase #3	$58.64	12.192%	$65.7894	$65.79	$65.80	$65.80
Purchase #4	$237.75	6.549%	$253.3202	$253.32	$253.30	$253.30
Purchase #5	$19.33	6.140%	$20.5169	$20.52	$20.50	$20.50
Purchase #6	$243.70	12.731%	$274.7254	$274.73	$274.75	$274.70
Purchase #7	$96.74	8.113%	$104.5885	$104.59	$104.60	$104.60
7 purchase totals =	$781.75		$851.1400	$851.15	$851.15	$851.10