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	$176.60	4.460%	$184.4764	$184.48	$184.50	$184.50
Purchase #2	$98.30	11.691%	$109.7923	$109.79	$109.80	$109.80
Purchase #3	$245.25	11.658%	$273.8412	$273.84	$273.85	$273.80
Purchase #4	$31.95	4.774%	$33.4753	$33.48	$33.50	$33.50
Purchase #5	$249.56	6.637%	$266.1233	$266.12	$266.10	$266.10
Purchase #6	$39.79	9.245%	$43.4686	$43.47	$43.45	$43.50
Purchase #7	$208.43	6.505%	$221.9884	$221.99	$222.00	$222.00
7 purchase totals =	$1,049.88		$1,133.1655	$1,133.17	$1,133.20	$1,133.20