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	$78.71	4.333%	$82.1205	$82.12	$82.10	$82.10
Purchase #2	$172.30	7.232%	$184.7607	$184.76	$184.75	$184.80
Purchase #3	$25.38	9.345%	$27.7518	$27.75	$27.75	$27.80
Purchase #4	$198.80	11.187%	$221.0398	$221.04	$221.05	$221.00
Purchase #5	$40.30	12.454%	$45.319	$45.32	$45.30	$45.30
Purchase #6	$136.55	12.250%	$153.2774	$153.28	$153.30	$153.30
Purchase #7	$169.55	3.743%	$175.8963	$175.90	$175.90	$175.90
7 purchase totals =	$821.59		$890.1655	$890.17	$890.15	$890.20