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	$239.92	6.681%	$255.9491	$255.95	$255.95	$255.90
Purchase #2	$181.88	10.178%	$200.3917	$200.39	$200.40	$200.40
Purchase #3	$75.47	4.708%	$79.0231	$79.02	$79.00	$79.00
Purchase #4	$240.82	5.753%	$254.6744	$254.67	$254.65	$254.70
Purchase #5	$75.84	8.424%	$82.2288	$82.23	$82.25	$82.20
Purchase #6	$127.50	11.614%	$142.3079	$142.31	$142.30	$142.30
Purchase #7	$208.85	8.372%	$226.3349	$226.33	$226.35	$226.30
7 purchase totals =	$1,150.28		$1,240.9099	$1,240.90	$1,240.90	$1,240.80