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	$160.32	6.386%	$170.558	$170.56	$170.55	$170.60
Purchase #2	$103.41	7.580%	$111.2485	$111.25	$111.25	$111.20
Purchase #3	$153.82	9.296%	$168.1191	$168.12	$168.10	$168.10
Purchase #4	$223.94	5.556%	$236.3821	$236.38	$236.40	$236.40
Purchase #5	$39.50	9.282%	$43.1664	$43.17	$43.15	$43.20
Purchase #6	$136.69	3.300%	$141.2008	$141.20	$141.20	$141.20
Purchase #7	$51.71	9.538%	$56.6421	$56.64	$56.65	$56.60
7 purchase totals =	$869.39		$927.3170	$927.32	$927.30	$927.30