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	$250.29	9.802%	$274.8234	$274.82	$274.80	$274.80
Purchase #2	$239.48	6.692%	$255.506	$255.51	$255.50	$255.50
Purchase #3	$93.49	7.436%	$100.4419	$100.44	$100.45	$100.40
Purchase #4	$225.55	5.620%	$238.2259	$238.23	$238.25	$238.20
Purchase #5	$245.33	4.751%	$256.9856	$256.99	$257.00	$257.00
Purchase #6	$124.43	13.592%	$141.3425	$141.34	$141.35	$141.30
Purchase #7	$90.94	12.781%	$102.563	$102.56	$102.55	$102.60
7 purchase totals =	$1,269.51		$1,369.8883	$1,369.89	$1,369.90	$1,369.80