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	$168.58	10.336%	$186.0044	$186.00	$186.00	$186.00
Purchase #2	$46.44	9.351%	$50.7826	$50.78	$50.80	$50.80
Purchase #3	$25.43	8.168%	$27.5071	$27.51	$27.50	$27.50
Purchase #4	$156.52	9.606%	$171.5553	$171.56	$171.55	$171.60
Purchase #5	$230.79	5.410%	$243.2757	$243.28	$243.30	$243.30
Purchase #6	$49.72	5.668%	$52.5381	$52.54	$52.55	$52.50
Purchase #7	$42.68	6.119%	$45.2916	$45.29	$45.30	$45.30
7 purchase totals =	$720.16		$776.9548	$776.96	$777.00	$777.00