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	$168.43	10.792%	$186.607	$186.61	$186.60	$186.60
Purchase #2	$51.86	13.810%	$59.0219	$59.02	$59.00	$59.00
Purchase #3	$31.78	12.781%	$35.8418	$35.84	$35.85	$35.80
Purchase #4	$56.51	4.654%	$59.14	$59.14	$59.15	$59.10
Purchase #5	$132.79	12.373%	$149.2201	$149.22	$149.20	$149.20
Purchase #6	$130.68	6.654%	$139.3754	$139.38	$139.40	$139.40
Purchase #7	$227.46	13.826%	$258.9086	$258.91	$258.90	$258.90
7 purchase totals =	$799.51		$888.1148	$888.12	$888.10	$888.00