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	$27.31	4.530%	$28.5471	$28.55	$28.55	$28.50
Purchase #2	$76.46	7.719%	$82.3619	$82.36	$82.35	$82.40
Purchase #3	$182.91	9.369%	$200.0468	$200.05	$200.05	$200.00
Purchase #4	$156.25	9.630%	$171.2969	$171.30	$171.30	$171.30
Purchase #5	$241.79	5.559%	$255.2311	$255.23	$255.25	$255.20
Purchase #6	$248.52	10.665%	$275.0247	$275.02	$275.00	$275.00
Purchase #7	$204.90	13.803%	$233.1823	$233.18	$233.20	$233.20
7 purchase totals =	$1,138.14		$1,245.6908	$1,245.69	$1,245.70	$1,245.60