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	$77.73	13.368%	$88.1209	$88.12	$88.10	$88.10
Purchase #2	$241.61	3.792%	$250.7719	$250.77	$250.75	$250.80
Purchase #3	$142.43	9.474%	$155.9238	$155.92	$155.90	$155.90
Purchase #4	$97.28	12.656%	$109.5918	$109.59	$109.60	$109.60
Purchase #5	$245.99	4.120%	$256.1248	$256.12	$256.10	$256.10
Purchase #6	$177.77	12.837%	$200.5903	$200.59	$200.60	$200.60
Purchase #7	$125.27	4.113%	$130.4224	$130.42	$130.40	$130.40
7 purchase totals =	$1,108.08		$1,191.5459	$1,191.53	$1,191.45	$1,191.50