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	$168.33	13.467%	$190.999	$191.00	$191.00	$191.00
Purchase #2	$206.43	11.464%	$230.0951	$230.10	$230.10	$230.10
Purchase #3	$79.78	12.488%	$89.7429	$89.74	$89.75	$89.70
Purchase #4	$204.44	10.426%	$225.7549	$225.75	$225.75	$225.80
Purchase #5	$208.33	11.310%	$231.8921	$231.89	$231.90	$231.90
Purchase #6	$20.32	7.298%	$21.803	$21.80	$21.80	$21.80
Purchase #7	$249.90	11.206%	$277.9038	$277.90	$277.90	$277.90
7 purchase totals =	$1,137.53		$1,268.1908	$1,268.18	$1,268.20	$1,268.20