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	$31.90	6.283%	$33.9043	$33.90	$33.90	$33.90
Purchase #2	$68.72	5.456%	$72.4694	$72.47	$72.45	$72.50
Purchase #3	$113.97	8.251%	$123.3737	$123.37	$123.35	$123.40
Purchase #4	$239.70	11.701%	$267.7473	$267.75	$267.75	$267.70
Purchase #5	$186.67	13.753%	$212.3427	$212.34	$212.35	$212.30
Purchase #6	$80.83	5.448%	$85.2336	$85.23	$85.25	$85.20
Purchase #7	$218.86	6.538%	$233.1691	$233.17	$233.15	$233.20
7 purchase totals =	$940.65		$1,028.2401	$1,028.23	$1,028.20	$1,028.20