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	$37.48	4.452%	$39.1486	$39.15	$39.15	$39.10
Purchase #2	$150.89	7.534%	$162.2581	$162.26	$162.25	$162.30
Purchase #3	$88.53	7.433%	$95.1104	$95.11	$95.10	$95.10
Purchase #4	$190.49	10.230%	$209.9771	$209.98	$210.00	$210.00
Purchase #5	$104.82	6.764%	$111.91	$111.91	$111.90	$111.90
Purchase #6	$249.31	13.340%	$282.568	$282.57	$282.55	$282.60
Purchase #7	$91.35	12.520%	$102.787	$102.79	$102.80	$102.80
7 purchase totals =	$912.87		$1,003.7592	$1,003.77	$1,003.75	$1,003.80