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	$35.76	7.216%	$38.3404	$38.34	$38.35	$38.30
Purchase #2	$128.89	6.852%	$137.7215	$137.72	$137.70	$137.70
Purchase #3	$223.79	9.445%	$244.927	$244.93	$244.95	$244.90
Purchase #4	$171.89	7.369%	$184.5566	$184.56	$184.55	$184.60
Purchase #5	$11.38	7.139%	$12.1924	$12.19	$12.20	$12.20
Purchase #6	$85.42	5.447%	$90.0728	$90.07	$90.05	$90.10
Purchase #7	$41.54	3.617%	$43.0425	$43.04	$43.05	$43.00
7 purchase totals =	$698.67		$750.8532	$750.85	$750.85	$750.80