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	$159.28	13.671%	$181.0552	$181.06	$181.05	$181.10
Purchase #2	$239.61	4.506%	$250.4068	$250.41	$250.40	$250.40
Purchase #3	$138.45	4.318%	$144.4283	$144.43	$144.45	$144.40
Purchase #4	$183.90	3.765%	$190.8238	$190.82	$190.80	$190.80
Purchase #5	$156.48	8.585%	$169.9138	$169.91	$169.90	$169.90
Purchase #6	$19.42	13.470%	$22.0359	$22.04	$22.05	$22.00
Purchase #7	$120.25	9.704%	$131.9191	$131.92	$131.90	$131.90
7 purchase totals =	$1,017.39		$1,090.5829	$1,090.59	$1,090.55	$1,090.50