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	$221.41	9.387%	$242.1938	$242.19	$242.20	$242.20
Purchase #2	$200.59	7.432%	$215.4978	$215.50	$215.50	$215.50
Purchase #3	$145.96	13.258%	$165.3114	$165.31	$165.30	$165.30
Purchase #4	$188.98	5.507%	$199.3871	$199.39	$199.40	$199.40
Purchase #5	$63.70	11.322%	$70.9121	$70.91	$70.90	$70.90
Purchase #6	$90.73	11.252%	$100.9389	$100.94	$100.95	$100.90
Purchase #7	$200.97	10.743%	$222.5602	$222.56	$222.55	$222.60
7 purchase totals =	$1,112.34		$1,216.8013	$1,216.80	$1,216.80	$1,216.80