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	$72.31	11.180%	$80.3943	$80.39	$80.40	$80.40
Purchase #2	$237.39	13.620%	$269.7225	$269.72	$269.70	$269.70
Purchase #3	$115.74	6.547%	$123.3175	$123.32	$123.30	$123.30
Purchase #4	$218.45	6.639%	$232.9529	$232.95	$232.95	$233.00
Purchase #5	$222.28	12.490%	$250.0428	$250.04	$250.05	$250.00
Purchase #6	$102.88	8.391%	$111.5127	$111.51	$111.50	$111.50
Purchase #7	$46.54	12.446%	$52.3324	$52.33	$52.35	$52.30
7 purchase totals =	$1,015.59		$1,120.2751	$1,120.26	$1,120.25	$1,120.20