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	$130.43	12.838%	$147.1746	$147.17	$147.15	$147.20
Purchase #2	$210.69	11.796%	$235.543	$235.54	$235.55	$235.50
Purchase #3	$82.90	8.792%	$90.1886	$90.19	$90.20	$90.20
Purchase #4	$18.36	4.311%	$19.1515	$19.15	$19.15	$19.20
Purchase #5	$204.56	8.565%	$222.0806	$222.08	$222.10	$222.10
Purchase #6	$136.76	3.840%	$142.0116	$142.01	$142.00	$142.00
Purchase #7	$75.83	12.638%	$85.4134	$85.41	$85.40	$85.40
7 purchase totals =	$859.53		$941.5633	$941.55	$941.55	$941.60