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	$144.81	3.744%	$150.2317	$150.23	$150.25	$150.20
Purchase #2	$122.74	4.318%	$128.0399	$128.04	$128.05	$128.00
Purchase #3	$240.36	13.187%	$272.0563	$272.06	$272.05	$272.10
Purchase #4	$209.92	6.646%	$223.8713	$223.87	$223.85	$223.90
Purchase #5	$111.39	12.577%	$125.3995	$125.40	$125.40	$125.40
Purchase #6	$75.25	11.368%	$83.8044	$83.80	$83.80	$83.80
Purchase #7	$198.63	7.425%	$213.3783	$213.38	$213.40	$213.40
7 purchase totals =	$1,103.10		$1,196.7814	$1,196.78	$1,196.80	$1,196.80