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	$65.53	11.811%	$73.2697	$73.27	$73.25	$73.30
Purchase #2	$181.84	5.258%	$191.4011	$191.40	$191.40	$191.40
Purchase #3	$83.36	7.369%	$89.5028	$89.50	$89.50	$89.50
Purchase #4	$176.43	5.344%	$185.8584	$185.86	$185.85	$185.90
Purchase #5	$123.25	6.486%	$131.244	$131.24	$131.25	$131.20
Purchase #6	$60.67	12.180%	$68.0596	$68.06	$68.05	$68.10
Purchase #7	$214.38	9.679%	$235.1298	$235.13	$235.15	$235.10
7 purchase totals =	$905.46		$974.4654	$974.46	$974.45	$974.50