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	$86.30	4.780%	$90.4251	$90.43	$90.45	$90.40
Purchase #2	$170.56	10.280%	$188.0936	$188.09	$188.10	$188.10
Purchase #3	$193.58	11.789%	$216.4011	$216.40	$216.40	$216.40
Purchase #4	$143.70	4.760%	$150.5401	$150.54	$150.55	$150.50
Purchase #5	$124.92	12.680%	$140.7599	$140.76	$140.75	$140.80
Purchase #6	$238.76	13.680%	$271.4224	$271.42	$271.40	$271.40
Purchase #7	$83.62	6.845%	$89.3438	$89.34	$89.35	$89.30
7 purchase totals =	$1,041.44		$1,146.9860	$1,146.98	$1,147.00	$1,146.90