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	$113.99	12.382%	$128.1042	$128.10	$128.10	$128.10
Purchase #2	$47.99	10.140%	$52.8562	$52.86	$52.85	$52.90
Purchase #3	$92.72	6.339%	$98.5975	$98.60	$98.60	$98.60
Purchase #4	$92.73	7.634%	$99.809	$99.81	$99.80	$99.80
Purchase #5	$84.28	6.538%	$89.7902	$89.79	$89.80	$89.80
Purchase #6	$40.56	6.641%	$43.2536	$43.25	$43.25	$43.30
Purchase #7	$81.33	9.320%	$88.91	$88.91	$88.90	$88.90
7 purchase totals =	$553.60		$601.3207	$601.32	$601.30	$601.40