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	$176.96	13.311%	$200.5151	$200.52	$200.50	$200.50
Purchase #2	$91.84	5.431%	$96.8278	$96.83	$96.85	$96.80
Purchase #3	$128.61	13.841%	$146.4109	$146.41	$146.40	$146.40
Purchase #4	$146.80	9.346%	$160.5199	$160.52	$160.50	$160.50
Purchase #5	$175.86	12.698%	$198.1907	$198.19	$198.20	$198.20
Purchase #6	$84.53	6.365%	$89.9103	$89.91	$89.90	$89.90
Purchase #7	$103.36	6.410%	$109.9854	$109.99	$110.00	$110.00
7 purchase totals =	$907.96		$1,002.3601	$1,002.37	$1,002.35	$1,002.30