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	$83.46	8.140%	$90.2536	$90.25	$90.25	$90.30
Purchase #2	$117.44	9.796%	$128.9444	$128.94	$128.95	$128.90
Purchase #3	$147.75	3.475%	$152.8843	$152.88	$152.90	$152.90
Purchase #4	$92.47	7.819%	$99.7002	$99.70	$99.70	$99.70
Purchase #5	$180.27	10.809%	$199.7554	$199.76	$199.75	$199.80
Purchase #6	$17.39	7.593%	$18.7104	$18.71	$18.70	$18.70
Purchase #7	$226.34	7.179%	$242.5889	$242.59	$242.60	$242.60
7 purchase totals =	$865.12		$932.8372	$932.83	$932.85	$932.90