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	$84.76	7.437%	$91.0636	$91.06	$91.05	$91.10
Purchase #2	$104.39	10.701%	$115.5608	$115.56	$115.55	$115.60
Purchase #3	$142.79	5.738%	$150.9833	$150.98	$151.00	$151.00
Purchase #4	$207.64	12.655%	$233.9168	$233.92	$233.90	$233.90
Purchase #5	$100.89	8.354%	$109.3184	$109.32	$109.30	$109.30
Purchase #6	$23.70	10.704%	$26.2368	$26.24	$26.25	$26.20
Purchase #7	$177.30	10.814%	$196.4732	$196.47	$196.45	$196.50
7 purchase totals =	$841.47		$923.5529	$923.55	$923.50	$923.60