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	$242.52	5.802%	$256.591	$256.59	$256.60	$256.60
Purchase #2	$215.62	10.372%	$237.9841	$237.98	$238.00	$238.00
Purchase #3	$83.62	5.871%	$88.5293	$88.53	$88.55	$88.50
Purchase #4	$25.34	12.843%	$28.5944	$28.59	$28.60	$28.60
Purchase #5	$190.59	12.384%	$214.1927	$214.19	$214.20	$214.20
Purchase #6	$67.28	13.123%	$76.1092	$76.11	$76.10	$76.10
Purchase #7	$170.57	11.357%	$189.9416	$189.94	$189.95	$189.90
7 purchase totals =	$995.54		$1,091.9423	$1,091.93	$1,092.00	$1,091.90