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	$39.42	7.128%	$42.2299	$42.23	$42.25	$42.20
Purchase #2	$85.98	4.753%	$90.0666	$90.07	$90.05	$90.10
Purchase #3	$25.87	4.455%	$27.0225	$27.02	$27.00	$27.00
Purchase #4	$223.96	10.629%	$247.7647	$247.76	$247.75	$247.80
Purchase #5	$248.59	6.504%	$264.7583	$264.76	$264.75	$264.80
Purchase #6	$168.42	11.345%	$187.5272	$187.53	$187.55	$187.50
Purchase #7	$215.84	3.574%	$223.5541	$223.55	$223.55	$223.60
7 purchase totals =	$1,008.08		$1,082.9233	$1,082.92	$1,082.90	$1,083.00