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	$38.54	9.873%	$42.3451	$42.35	$42.35	$42.30
Purchase #2	$69.29	8.701%	$75.3189	$75.32	$75.30	$75.30
Purchase #3	$175.77	11.808%	$196.5249	$196.52	$196.50	$196.50
Purchase #4	$26.94	5.833%	$28.5114	$28.51	$28.50	$28.50
Purchase #5	$26.59	3.407%	$27.4959	$27.50	$27.50	$27.50
Purchase #6	$73.84	9.333%	$80.7315	$80.73	$80.75	$80.70
Purchase #7	$145.92	3.135%	$150.4946	$150.49	$150.50	$150.50
7 purchase totals =	$556.89		$601.4223	$601.42	$601.40	$601.30