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	$85.35	5.353%	$89.9188	$89.92	$89.90	$89.90
Purchase #2	$237.32	13.794%	$270.0559	$270.06	$270.05	$270.10
Purchase #3	$173.26	11.458%	$193.1121	$193.11	$193.10	$193.10
Purchase #4	$245.46	3.259%	$253.4595	$253.46	$253.45	$253.50
Purchase #5	$98.57	10.820%	$109.2353	$109.24	$109.25	$109.20
Purchase #6	$70.31	11.508%	$78.4013	$78.40	$78.40	$78.40
Purchase #7	$62.35	12.656%	$70.241	$70.24	$70.25	$70.20
7 purchase totals =	$972.62		$1,064.4239	$1,064.43	$1,064.40	$1,064.40