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	$36.57	11.472%	$40.7653	$40.77	$40.75	$40.80
Purchase #2	$94.97	9.381%	$103.8791	$103.88	$103.90	$103.90
Purchase #3	$44.31	6.488%	$47.1848	$47.18	$47.20	$47.20
Purchase #4	$137.36	13.515%	$155.9242	$155.92	$155.90	$155.90
Purchase #5	$200.34	9.404%	$219.18	$219.18	$219.20	$219.20
Purchase #6	$211.44	5.539%	$223.1517	$223.15	$223.15	$223.20
Purchase #7	$187.46	11.662%	$209.3216	$209.32	$209.30	$209.30
7 purchase totals =	$912.45		$999.4067	$999.40	$999.40	$999.50