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	$70.83	11.228%	$78.7828	$78.78	$78.80	$78.80
Purchase #2	$135.27	11.667%	$151.052	$151.05	$151.05	$151.10
Purchase #3	$137.53	6.625%	$146.6414	$146.64	$146.65	$146.60
Purchase #4	$84.55	11.278%	$94.0855	$94.09	$94.10	$94.10
Purchase #5	$73.75	11.470%	$82.2091	$82.21	$82.20	$82.20
Purchase #6	$174.78	12.376%	$196.4108	$196.41	$196.40	$196.40
Purchase #7	$62.84	10.850%	$69.6581	$69.66	$69.65	$69.70
7 purchase totals =	$739.55		$818.8397	$818.84	$818.85	$818.90