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	$122.79	5.462%	$129.4968	$129.50	$129.50	$129.50
Purchase #2	$184.96	5.575%	$195.2715	$195.27	$195.25	$195.30
Purchase #3	$208.28	11.166%	$231.5365	$231.54	$231.55	$231.50
Purchase #4	$82.38	9.158%	$89.9244	$89.92	$89.90	$89.90
Purchase #5	$196.97	9.272%	$215.2331	$215.23	$215.25	$215.20
Purchase #6	$179.68	11.824%	$200.9254	$200.93	$200.95	$200.90
Purchase #7	$90.43	10.398%	$99.8329	$99.83	$99.85	$99.80
7 purchase totals =	$1,065.49		$1,162.2206	$1,162.22	$1,162.25	$1,162.10