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	$229.71	12.229%	$257.8012	$257.80	$257.80	$257.80
Purchase #2	$110.50	11.717%	$123.4473	$123.45	$123.45	$123.40
Purchase #3	$70.46	11.760%	$78.7461	$78.75	$78.75	$78.70
Purchase #4	$102.88	9.205%	$112.3501	$112.35	$112.35	$112.40
Purchase #5	$169.89	13.148%	$192.2271	$192.23	$192.25	$192.20
Purchase #6	$86.95	3.834%	$90.2837	$90.28	$90.30	$90.30
Purchase #7	$168.56	8.756%	$183.3191	$183.32	$183.30	$183.30
7 purchase totals =	$938.95		$1,038.1746	$1,038.18	$1,038.20	$1,038.10