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	$55.62	12.753%	$62.7132	$62.71	$62.70	$62.70
Purchase #2	$73.49	9.600%	$80.545	$80.55	$80.55	$80.50
Purchase #3	$64.88	12.171%	$72.7765	$72.78	$72.80	$72.80
Purchase #4	$135.27	7.141%	$144.9296	$144.93	$144.95	$144.90
Purchase #5	$221.49	7.642%	$238.4163	$238.42	$238.40	$238.40
Purchase #6	$63.61	13.557%	$72.2336	$72.23	$72.25	$72.20
Purchase #7	$142.69	12.528%	$160.5662	$160.57	$160.55	$160.60
7 purchase totals =	$757.05		$832.1804	$832.19	$832.20	$832.10