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	$72.84	8.265%	$78.8602	$78.86	$78.85	$78.90
Purchase #2	$223.63	11.148%	$248.5603	$248.56	$248.55	$248.60
Purchase #3	$208.73	6.513%	$222.3246	$222.32	$222.30	$222.30
Purchase #4	$40.28	11.235%	$44.8055	$44.81	$44.80	$44.80
Purchase #5	$152.81	9.833%	$167.8358	$167.84	$167.85	$167.80
Purchase #6	$38.65	9.780%	$42.43	$42.43	$42.45	$42.40
Purchase #7	$42.91	6.453%	$45.679	$45.68	$45.70	$45.70
7 purchase totals =	$779.85		$850.4954	$850.50	$850.50	$850.50