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	$84.53	9.212%	$92.3169	$92.32	$92.30	$92.30
Purchase #2	$234.84	11.681%	$262.2717	$262.27	$262.25	$262.30
Purchase #3	$145.48	3.340%	$150.339	$150.34	$150.35	$150.30
Purchase #4	$118.90	8.186%	$128.6332	$128.63	$128.65	$128.60
Purchase #5	$48.30	13.339%	$54.7427	$54.74	$54.75	$54.70
Purchase #6	$171.81	11.562%	$191.6747	$191.67	$191.65	$191.70
Purchase #7	$55.56	7.776%	$59.8803	$59.88	$59.90	$59.90
7 purchase totals =	$859.42		$939.8585	$939.85	$939.85	$939.80