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	$127.58	11.807%	$142.6434	$142.64	$142.65	$142.60
Purchase #2	$133.50	6.585%	$142.291	$142.29	$142.30	$142.30
Purchase #3	$154.91	9.663%	$169.879	$169.88	$169.90	$169.90
Purchase #4	$75.69	12.741%	$85.3337	$85.33	$85.35	$85.30
Purchase #5	$133.39	8.417%	$144.6174	$144.62	$144.60	$144.60
Purchase #6	$6.98	7.276%	$7.4879	$7.49	$7.50	$7.50
Purchase #7	$65.96	3.360%	$68.1763	$68.18	$68.20	$68.20
7 purchase totals =	$698.01		$760.4287	$760.43	$760.50	$760.40