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	$79.48	3.444%	$82.2173	$82.22	$82.20	$82.20
Purchase #2	$69.25	9.161%	$75.594	$75.59	$75.60	$75.60
Purchase #3	$78.51	8.313%	$85.0365	$85.04	$85.05	$85.00
Purchase #4	$185.27	11.425%	$206.4371	$206.44	$206.45	$206.40
Purchase #5	$125.59	12.659%	$141.4884	$141.49	$141.50	$141.50
Purchase #6	$76.48	7.507%	$82.2214	$82.22	$82.20	$82.20
Purchase #7	$149.96	4.288%	$156.3903	$156.39	$156.40	$156.40
7 purchase totals =	$764.54		$829.3850	$829.39	$829.40	$829.30