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	$73.46	6.838%	$78.4832	$78.48	$78.50	$78.50
Purchase #2	$58.38	3.415%	$60.3737	$60.37	$60.35	$60.40
Purchase #3	$38.76	9.160%	$42.3104	$42.31	$42.30	$42.30
Purchase #4	$181.76	6.171%	$192.9764	$192.98	$193.00	$193.00
Purchase #5	$6.64	11.295%	$7.39	$7.39	$7.40	$7.40
Purchase #6	$49.64	13.619%	$56.4005	$56.40	$56.40	$56.40
Purchase #7	$135.61	10.623%	$150.0159	$150.02	$150.00	$150.00
7 purchase totals =	$544.25		$587.9501	$587.95	$587.95	$588.00