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	$174.81	12.664%	$196.9479	$196.95	$196.95	$196.90
Purchase #2	$35.98	11.695%	$40.1879	$40.19	$40.20	$40.20
Purchase #3	$130.57	9.789%	$143.3515	$143.35	$143.35	$143.40
Purchase #4	$144.60	3.641%	$149.8649	$149.86	$149.85	$149.90
Purchase #5	$229.78	4.814%	$240.8416	$240.84	$240.85	$240.80
Purchase #6	$32.84	6.590%	$35.0042	$35.00	$35.00	$35.00
Purchase #7	$38.45	10.676%	$42.5549	$42.55	$42.55	$42.60
7 purchase totals =	$787.03		$848.7529	$848.74	$848.75	$848.80