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	$132.85	3.494%	$137.4918	$137.49	$137.50	$137.50
Purchase #2	$150.98	8.640%	$164.0247	$164.02	$164.00	$164.00
Purchase #3	$174.28	5.330%	$183.5691	$183.57	$183.55	$183.60
Purchase #4	$49.46	5.599%	$52.2293	$52.23	$52.25	$52.20
Purchase #5	$187.58	11.353%	$208.876	$208.88	$208.90	$208.90
Purchase #6	$58.50	5.155%	$61.5157	$61.52	$61.50	$61.50
Purchase #7	$42.61	7.596%	$45.8467	$45.85	$45.85	$45.80
7 purchase totals =	$796.26		$853.5533	$853.56	$853.55	$853.50