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	$180.49	4.651%	$188.8846	$188.88	$188.90	$188.90
Purchase #2	$19.29	3.306%	$19.9277	$19.93	$19.95	$19.90
Purchase #3	$166.81	11.397%	$185.8213	$185.82	$185.80	$185.80
Purchase #4	$86.29	8.374%	$93.5159	$93.52	$93.50	$93.50
Purchase #5	$98.71	6.266%	$104.8952	$104.90	$104.90	$104.90
Purchase #6	$192.36	11.315%	$214.1255	$214.13	$214.15	$214.10
Purchase #7	$198.57	5.668%	$209.8249	$209.82	$209.80	$209.80
7 purchase totals =	$942.52		$1,016.9951	$1,017.00	$1,017.00	$1,016.90