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	$76.47	12.823%	$86.2757	$86.28	$86.30	$86.30
Purchase #2	$165.98	12.596%	$186.8868	$186.89	$186.90	$186.90
Purchase #3	$41.96	13.342%	$47.5583	$47.56	$47.55	$47.60
Purchase #4	$96.89	4.761%	$101.5029	$101.50	$101.50	$101.50
Purchase #5	$205.75	12.783%	$232.051	$232.05	$232.05	$232.10
Purchase #6	$175.86	7.194%	$188.5114	$188.51	$188.50	$188.50
Purchase #7	$25.74	12.262%	$28.8962	$28.90	$28.90	$28.90
7 purchase totals =	$788.65		$871.6823	$871.69	$871.70	$871.80