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	$137.37	3.655%	$142.3909	$142.39	$142.40	$142.40
Purchase #2	$174.32	5.424%	$183.7751	$183.78	$183.80	$183.80
Purchase #3	$102.49	3.812%	$106.3969	$106.40	$106.40	$106.40
Purchase #4	$116.65	12.201%	$130.8825	$130.88	$130.90	$130.90
Purchase #5	$96.47	13.386%	$109.3835	$109.38	$109.40	$109.40
Purchase #6	$200.36	4.629%	$209.6347	$209.63	$209.65	$209.60
Purchase #7	$223.37	4.684%	$233.8327	$233.83	$233.85	$233.80
7 purchase totals =	$1,051.03		$1,116.2963	$1,116.29	$1,116.40	$1,116.30