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	$172.93	7.740%	$186.3148	$186.31	$186.30	$186.30
Purchase #2	$118.55	11.402%	$132.0671	$132.07	$132.05	$132.10
Purchase #3	$77.28	10.486%	$85.3836	$85.38	$85.40	$85.40
Purchase #4	$109.62	5.121%	$115.2336	$115.23	$115.25	$115.20
Purchase #5	$85.78	4.843%	$89.9343	$89.93	$89.95	$89.90
Purchase #6	$80.90	9.174%	$88.3218	$88.32	$88.30	$88.30
Purchase #7	$154.39	6.389%	$164.254	$164.25	$164.25	$164.30
7 purchase totals =	$799.45		$861.5092	$861.49	$861.50	$861.50