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	$72.33	11.187%	$80.4216	$80.42	$80.40	$80.40
Purchase #2	$99.32	6.451%	$105.7271	$105.73	$105.75	$105.70
Purchase #3	$121.52	11.556%	$135.5629	$135.56	$135.55	$135.60
Purchase #4	$64.29	4.705%	$67.3148	$67.31	$67.30	$67.30
Purchase #5	$167.76	12.373%	$188.5169	$188.52	$188.50	$188.50
Purchase #6	$174.28	4.707%	$182.4834	$182.48	$182.50	$182.50
Purchase #7	$213.56	12.137%	$239.4798	$239.48	$239.50	$239.50
7 purchase totals =	$913.06		$999.5065	$999.50	$999.50	$999.50