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	$151.69	12.712%	$170.9728	$170.97	$170.95	$171.00
Purchase #2	$82.42	9.234%	$90.0307	$90.03	$90.05	$90.00
Purchase #3	$233.54	13.859%	$265.9063	$265.91	$265.90	$265.90
Purchase #4	$100.61	9.320%	$109.9869	$109.99	$110.00	$110.00
Purchase #5	$78.94	4.654%	$82.6139	$82.61	$82.60	$82.60
Purchase #6	$98.25	7.167%	$105.2916	$105.29	$105.30	$105.30
Purchase #7	$150.73	12.317%	$169.2954	$169.30	$169.30	$169.30
7 purchase totals =	$896.18		$994.0976	$994.10	$994.10	$994.10