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	$90.27	13.249%	$102.2299	$102.23	$102.25	$102.20
Purchase #2	$146.33	12.590%	$164.7529	$164.75	$164.75	$164.80
Purchase #3	$34.67	7.488%	$37.2661	$37.27	$37.25	$37.30
Purchase #4	$197.41	9.228%	$215.627	$215.63	$215.65	$215.60
Purchase #5	$37.77	13.603%	$42.9079	$42.91	$42.90	$42.90
Purchase #6	$101.28	8.138%	$109.5222	$109.52	$109.50	$109.50
Purchase #7	$92.65	5.777%	$98.0024	$98.00	$98.00	$98.00
7 purchase totals =	$700.38		$770.3084	$770.31	$770.30	$770.30