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	$222.93	11.815%	$249.2692	$249.27	$249.25	$249.30
Purchase #2	$169.39	7.311%	$181.7741	$181.77	$181.75	$181.80
Purchase #3	$244.63	13.529%	$277.726	$277.73	$277.75	$277.70
Purchase #4	$172.71	10.849%	$191.4473	$191.45	$191.45	$191.40
Purchase #5	$85.98	4.610%	$89.9437	$89.94	$89.95	$89.90
Purchase #6	$39.72	4.609%	$41.5507	$41.55	$41.55	$41.60
Purchase #7	$138.43	11.745%	$154.6886	$154.69	$154.70	$154.70
7 purchase totals =	$1,073.79		$1,186.3996	$1,186.40	$1,186.40	$1,186.40