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	$131.25	6.755%	$140.1159	$140.12	$140.10	$140.10
Purchase #2	$35.70	8.275%	$38.6542	$38.65	$38.65	$38.70
Purchase #3	$229.94	7.478%	$247.1349	$247.13	$247.15	$247.10
Purchase #4	$155.42	8.389%	$168.4582	$168.46	$168.45	$168.50
Purchase #5	$228.95	11.539%	$255.3685	$255.37	$255.35	$255.40
Purchase #6	$250.65	13.830%	$285.3149	$285.31	$285.30	$285.30
Purchase #7	$78.84	13.464%	$89.455	$89.46	$89.45	$89.50
7 purchase totals =	$1,110.75		$1,224.5016	$1,224.50	$1,224.45	$1,224.60