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	$83.58	4.783%	$87.5776	$87.58	$87.60	$87.60
Purchase #2	$64.29	12.374%	$72.2452	$72.25	$72.25	$72.20
Purchase #3	$31.83	11.617%	$35.5277	$35.53	$35.55	$35.50
Purchase #4	$190.35	4.601%	$199.108	$199.11	$199.10	$199.10
Purchase #5	$227.42	9.612%	$249.2796	$249.28	$249.30	$249.30
Purchase #6	$150.82	11.394%	$168.0044	$168.00	$168.00	$168.00
Purchase #7	$99.97	9.145%	$109.1123	$109.11	$109.10	$109.10
7 purchase totals =	$848.26		$920.8548	$920.86	$920.90	$920.80