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	$98.54	11.361%	$109.7351	$109.74	$109.75	$109.70
Purchase #2	$54.76	8.589%	$59.4633	$59.46	$59.45	$59.50
Purchase #3	$109.98	3.335%	$113.6478	$113.65	$113.65	$113.60
Purchase #4	$150.70	11.395%	$167.8723	$167.87	$167.85	$167.90
Purchase #5	$220.52	9.700%	$241.9104	$241.91	$241.90	$241.90
Purchase #6	$67.29	7.477%	$72.3213	$72.32	$72.30	$72.30
Purchase #7	$63.56	12.205%	$71.3175	$71.32	$71.30	$71.30
7 purchase totals =	$765.35		$836.2677	$836.27	$836.20	$836.20