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	$136.96	13.419%	$155.3387	$155.34	$155.35	$155.30
Purchase #2	$81.64	11.354%	$90.9094	$90.91	$90.90	$90.90
Purchase #3	$100.56	10.871%	$111.4919	$111.49	$111.50	$111.50
Purchase #4	$179.44	8.736%	$195.1159	$195.12	$195.10	$195.10
Purchase #5	$211.27	3.126%	$217.8743	$217.87	$217.85	$217.90
Purchase #6	$92.43	11.399%	$102.9661	$102.97	$102.95	$103.00
Purchase #7	$102.25	12.817%	$115.3554	$115.36	$115.35	$115.40
7 purchase totals =	$904.55		$989.0517	$989.06	$989.00	$989.10