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	$77.92	5.400%	$82.1277	$82.13	$82.15	$82.10
Purchase #2	$58.83	5.846%	$62.2692	$62.27	$62.25	$62.30
Purchase #3	$123.88	7.708%	$133.4287	$133.43	$133.45	$133.40
Purchase #4	$109.53	9.501%	$119.9364	$119.94	$119.95	$119.90
Purchase #5	$52.96	6.474%	$56.3886	$56.39	$56.40	$56.40
Purchase #6	$192.61	12.437%	$216.5649	$216.56	$216.55	$216.60
Purchase #7	$206.85	9.793%	$227.1068	$227.11	$227.10	$227.10
7 purchase totals =	$822.58		$897.8223	$897.83	$897.85	$897.80