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	$235.44	6.211%	$250.0632	$250.06	$250.05	$250.10
Purchase #2	$72.66	8.194%	$78.6138	$78.61	$78.60	$78.60
Purchase #3	$202.62	3.550%	$209.813	$209.81	$209.80	$209.80
Purchase #4	$140.61	10.863%	$155.8845	$155.88	$155.90	$155.90
Purchase #5	$72.38	8.515%	$78.5432	$78.54	$78.55	$78.50
Purchase #6	$151.75	11.527%	$169.2422	$169.24	$169.25	$169.20
Purchase #7	$145.33	12.498%	$163.4933	$163.49	$163.50	$163.50
7 purchase totals =	$1,020.79		$1,105.6532	$1,105.63	$1,105.65	$1,105.60