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	$44.71	12.500%	$50.2988	$50.30	$50.30	$50.30
Purchase #2	$37.72	9.847%	$41.4343	$41.43	$41.45	$41.40
Purchase #3	$46.43	4.182%	$48.3717	$48.37	$48.35	$48.40
Purchase #4	$237.31	12.740%	$267.5433	$267.54	$267.55	$267.50
Purchase #5	$243.52	12.178%	$273.1759	$273.18	$273.20	$273.20
Purchase #6	$174.90	4.423%	$182.6358	$182.64	$182.65	$182.60
Purchase #7	$160.27	11.320%	$178.4126	$178.41	$178.40	$178.40
7 purchase totals =	$944.86		$1,041.8724	$1,041.87	$1,041.90	$1,041.80