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	$180.77	13.123%	$204.4924	$204.49	$204.50	$204.50
Purchase #2	$6.71	4.852%	$7.0356	$7.04	$7.05	$7.00
Purchase #3	$78.76	4.223%	$82.086	$82.09	$82.10	$82.10
Purchase #4	$85.28	13.681%	$96.9472	$96.95	$96.95	$96.90
Purchase #5	$102.92	7.111%	$110.2386	$110.24	$110.25	$110.20
Purchase #6	$209.40	6.391%	$222.7828	$222.78	$222.80	$222.80
Purchase #7	$125.66	10.870%	$139.3192	$139.32	$139.30	$139.30
7 purchase totals =	$789.50		$862.9018	$862.91	$862.95	$862.80