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	$77.78	3.362%	$80.395	$80.40	$80.40	$80.40
Purchase #2	$226.45	3.263%	$233.8391	$233.84	$233.85	$233.80
Purchase #3	$114.28	12.338%	$128.3799	$128.38	$128.40	$128.40
Purchase #4	$31.58	11.760%	$35.2938	$35.29	$35.30	$35.30
Purchase #5	$28.89	9.655%	$31.6793	$31.68	$31.70	$31.70
Purchase #6	$165.27	10.822%	$183.1555	$183.16	$183.15	$183.20
Purchase #7	$85.39	7.293%	$91.6175	$91.62	$91.60	$91.60
7 purchase totals =	$729.64		$784.3601	$784.37	$784.40	$784.40