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	$27.56	4.347%	$28.758	$28.76	$28.75	$28.80
Purchase #2	$233.88	11.637%	$261.0966	$261.10	$261.10	$261.10
Purchase #3	$81.58	9.422%	$89.2665	$89.27	$89.25	$89.30
Purchase #4	$159.98	9.844%	$175.7284	$175.73	$175.75	$175.70
Purchase #5	$193.45	8.498%	$209.8894	$209.89	$209.90	$209.90
Purchase #6	$58.96	7.562%	$63.4186	$63.42	$63.40	$63.40
Purchase #7	$170.50	10.762%	$188.8492	$188.85	$188.85	$188.80
7 purchase totals =	$925.91		$1,017.0067	$1,017.02	$1,017.00	$1,017.00