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	$156.74	9.428%	$171.5174	$171.52	$171.50	$171.50
Purchase #2	$210.30	8.823%	$228.8548	$228.85	$228.85	$228.90
Purchase #3	$57.97	5.628%	$61.2326	$61.23	$61.25	$61.20
Purchase #4	$49.88	7.330%	$53.5362	$53.54	$53.55	$53.50
Purchase #5	$223.44	11.666%	$249.5065	$249.51	$249.50	$249.50
Purchase #6	$64.96	7.553%	$69.8664	$69.87	$69.85	$69.90
Purchase #7	$145.61	3.615%	$150.8738	$150.87	$150.85	$150.90
7 purchase totals =	$908.90		$985.3877	$985.39	$985.35	$985.40