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	$245.83	7.118%	$263.3282	$263.33	$263.35	$263.30
Purchase #2	$172.54	10.621%	$190.8655	$190.87	$190.85	$190.90
Purchase #3	$109.61	9.837%	$120.3923	$120.39	$120.40	$120.40
Purchase #4	$196.48	5.839%	$207.9525	$207.95	$207.95	$208.00
Purchase #5	$134.46	8.514%	$145.9079	$145.91	$145.90	$145.90
Purchase #6	$41.88	11.593%	$46.7351	$46.74	$46.75	$46.70
Purchase #7	$24.96	12.104%	$27.9812	$27.98	$28.00	$28.00
7 purchase totals =	$925.76		$1,003.1627	$1,003.17	$1,003.20	$1,003.20