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	$73.27	11.802%	$81.9173	$81.92	$81.90	$81.90
Purchase #2	$72.91	12.614%	$82.1069	$82.11	$82.10	$82.10
Purchase #3	$111.57	3.351%	$115.3087	$115.31	$115.30	$115.30
Purchase #4	$98.84	6.802%	$105.5631	$105.56	$105.55	$105.60
Purchase #5	$38.30	11.829%	$42.8305	$42.83	$42.85	$42.80
Purchase #6	$156.64	12.500%	$176.22	$176.22	$176.20	$176.20
Purchase #7	$91.70	5.689%	$96.9168	$96.92	$96.90	$96.90
7 purchase totals =	$643.23		$700.8633	$700.87	$700.80	$700.80