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	$250.96	7.828%	$270.6051	$270.61	$270.60	$270.60
Purchase #2	$200.86	5.440%	$211.7868	$211.79	$211.80	$211.80
Purchase #3	$99.74	9.404%	$109.1195	$109.12	$109.10	$109.10
Purchase #4	$72.82	7.556%	$78.3223	$78.32	$78.30	$78.30
Purchase #5	$249.93	5.741%	$264.2785	$264.28	$264.30	$264.30
Purchase #6	$59.47	8.123%	$64.3007	$64.30	$64.30	$64.30
Purchase #7	$153.36	12.127%	$171.958	$171.96	$171.95	$172.00
7 purchase totals =	$1,087.14		$1,170.3709	$1,170.38	$1,170.35	$1,170.40