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	$120.63	6.217%	$128.1296	$128.13	$128.15	$128.10
Purchase #2	$17.69	12.857%	$19.9644	$19.96	$19.95	$20.00
Purchase #3	$226.31	12.198%	$253.9153	$253.92	$253.90	$253.90
Purchase #4	$75.45	10.856%	$83.6409	$83.64	$83.65	$83.60
Purchase #5	$40.51	4.490%	$42.3289	$42.33	$42.35	$42.30
Purchase #6	$168.98	12.765%	$190.5503	$190.55	$190.55	$190.60
Purchase #7	$62.55	7.607%	$67.3082	$67.31	$67.30	$67.30
7 purchase totals =	$712.12		$785.8376	$785.84	$785.85	$785.80