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	$203.88	4.383%	$212.8161	$212.82	$212.80	$212.80
Purchase #2	$79.70	12.541%	$89.6952	$89.70	$89.70	$89.70
Purchase #3	$231.77	9.825%	$254.5414	$254.54	$254.55	$254.50
Purchase #4	$178.70	9.871%	$196.3395	$196.34	$196.35	$196.30
Purchase #5	$197.46	3.618%	$204.6041	$204.60	$204.60	$204.60
Purchase #6	$49.28	13.404%	$55.8855	$55.89	$55.90	$55.90
Purchase #7	$87.29	3.200%	$90.0833	$90.08	$90.10	$90.10
7 purchase totals =	$1,028.08		$1,103.9651	$1,103.97	$1,104.00	$1,103.90