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	$17.92	7.839%	$19.3247	$19.32	$19.30	$19.30
Purchase #2	$216.43	8.139%	$234.0452	$234.05	$234.05	$234.00
Purchase #3	$73.94	6.201%	$78.525	$78.53	$78.55	$78.50
Purchase #4	$37.32	13.399%	$42.3205	$42.32	$42.30	$42.30
Purchase #5	$202.70	7.562%	$218.0282	$218.03	$218.05	$218.00
Purchase #6	$116.64	8.474%	$126.5241	$126.52	$126.50	$126.50
Purchase #7	$86.66	3.325%	$89.5414	$89.54	$89.55	$89.50
7 purchase totals =	$751.61		$808.3091	$808.31	$808.30	$808.10