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	$36.35	12.145%	$40.7647	$40.76	$40.75	$40.80
Purchase #2	$39.61	6.312%	$42.1102	$42.11	$42.10	$42.10
Purchase #3	$67.72	4.219%	$70.5771	$70.58	$70.60	$70.60
Purchase #4	$76.92	4.481%	$80.3668	$80.37	$80.35	$80.40
Purchase #5	$135.56	4.656%	$141.8717	$141.87	$141.85	$141.90
Purchase #6	$166.42	4.657%	$174.1702	$174.17	$174.15	$174.20
Purchase #7	$75.80	12.106%	$84.9763	$84.98	$85.00	$85.00
7 purchase totals =	$598.38		$634.8370	$634.84	$634.80	$635.00