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	$221.28	3.170%	$228.2946	$228.29	$228.30	$228.30
Purchase #2	$129.92	7.638%	$139.8433	$139.84	$139.85	$139.80
Purchase #3	$191.41	11.681%	$213.7686	$213.77	$213.75	$213.80
Purchase #4	$148.49	7.158%	$159.1189	$159.12	$159.10	$159.10
Purchase #5	$35.93	5.430%	$37.881	$37.88	$37.90	$37.90
Purchase #6	$240.43	13.675%	$273.3088	$273.31	$273.30	$273.30
Purchase #7	$92.31	3.403%	$95.4513	$95.45	$95.45	$95.50
7 purchase totals =	$1,059.77		$1,147.6665	$1,147.66	$1,147.65	$1,147.70