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	$181.39	4.415%	$189.3984	$189.40	$189.40	$189.40
Purchase #2	$124.32	10.624%	$137.5278	$137.53	$137.55	$137.50
Purchase #3	$115.51	10.830%	$128.0197	$128.02	$128.00	$128.00
Purchase #4	$62.44	7.555%	$67.1573	$67.16	$67.15	$67.20
Purchase #5	$88.69	8.749%	$96.4495	$96.45	$96.45	$96.40
Purchase #6	$209.71	7.553%	$225.5494	$225.55	$225.55	$225.50
Purchase #7	$228.40	7.223%	$244.8973	$244.90	$244.90	$244.90
7 purchase totals =	$1,010.46		$1,088.9994	$1,089.01	$1,089.00	$1,088.90