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	$203.52	10.818%	$225.5368	$225.54	$225.55	$225.50
Purchase #2	$98.29	7.661%	$105.82	$105.82	$105.80	$105.80
Purchase #3	$28.36	7.361%	$30.4476	$30.45	$30.45	$30.40
Purchase #4	$90.52	13.274%	$102.5356	$102.54	$102.55	$102.50
Purchase #5	$49.40	11.376%	$55.0197	$55.02	$55.00	$55.00
Purchase #6	$29.31	12.655%	$33.0192	$33.02	$33.00	$33.00
Purchase #7	$100.35	9.663%	$110.0468	$110.05	$110.05	$110.00
7 purchase totals =	$599.75		$662.4257	$662.44	$662.40	$662.20