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	$132.38	4.186%	$137.9214	$137.92	$137.90	$137.90
Purchase #2	$248.35	7.711%	$267.5003	$267.50	$267.50	$267.50
Purchase #3	$79.29	3.843%	$82.3371	$82.34	$82.35	$82.30
Purchase #4	$127.30	8.220%	$137.7641	$137.76	$137.75	$137.80
Purchase #5	$23.85	5.220%	$25.095	$25.10	$25.10	$25.10
Purchase #6	$158.91	4.163%	$165.5254	$165.53	$165.55	$165.50
Purchase #7	$167.88	8.628%	$182.3647	$182.36	$182.35	$182.40
7 purchase totals =	$937.96		$998.5080	$998.51	$998.50	$998.50