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	$178.49	5.565%	$188.423	$188.42	$188.40	$188.40
Purchase #2	$82.75	9.770%	$90.8347	$90.83	$90.85	$90.80
Purchase #3	$238.71	4.204%	$248.7454	$248.75	$248.75	$248.70
Purchase #4	$243.90	12.563%	$274.5412	$274.54	$274.55	$274.50
Purchase #5	$194.43	8.660%	$211.2676	$211.27	$211.25	$211.30
Purchase #6	$18.41	9.755%	$20.2059	$20.21	$20.20	$20.20
Purchase #7	$150.98	9.711%	$165.6417	$165.64	$165.65	$165.60
7 purchase totals =	$1,107.67		$1,199.6595	$1,199.66	$1,199.65	$1,199.50