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	$72.43	13.454%	$82.1747	$82.17	$82.15	$82.20
Purchase #2	$96.35	9.203%	$105.2171	$105.22	$105.20	$105.20
Purchase #3	$53.59	12.647%	$60.3675	$60.37	$60.35	$60.40
Purchase #4	$25.69	4.846%	$26.9349	$26.93	$26.95	$26.90
Purchase #5	$171.87	10.191%	$189.3853	$189.39	$189.40	$189.40
Purchase #6	$134.29	7.486%	$144.3429	$144.34	$144.35	$144.30
Purchase #7	$20.31	7.425%	$21.818	$21.82	$21.80	$21.80
7 purchase totals =	$574.53		$630.2404	$630.24	$630.20	$630.20