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	$83.83	9.760%	$92.0118	$92.01	$92.00	$92.00
Purchase #2	$142.60	11.500%	$158.999	$159.00	$159.00	$159.00
Purchase #3	$82.31	12.781%	$92.83	$92.83	$92.85	$92.80
Purchase #4	$144.41	8.297%	$156.3917	$156.39	$156.40	$156.40
Purchase #5	$67.39	7.499%	$72.4436	$72.44	$72.45	$72.40
Purchase #6	$121.83	13.400%	$138.1552	$138.16	$138.15	$138.20
Purchase #7	$68.30	7.370%	$73.3337	$73.33	$73.35	$73.30
7 purchase totals =	$710.67		$784.1650	$784.16	$784.20	$784.10