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	$180.35	4.530%	$188.5199	$188.52	$188.50	$188.50
Purchase #2	$72.75	10.705%	$80.5379	$80.54	$80.55	$80.50
Purchase #3	$51.57	6.859%	$55.1072	$55.11	$55.10	$55.10
Purchase #4	$57.57	11.865%	$64.4007	$64.40	$64.40	$64.40
Purchase #5	$212.39	9.589%	$232.7561	$232.76	$232.75	$232.80
Purchase #6	$103.34	7.510%	$111.1008	$111.10	$111.10	$111.10
Purchase #7	$31.26	6.505%	$33.2935	$33.29	$33.30	$33.30
7 purchase totals =	$709.23		$765.7161	$765.72	$765.70	$765.70