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	$183.74	13.700%	$208.9124	$208.91	$208.90	$208.90
Purchase #2	$78.89	7.843%	$85.0773	$85.08	$85.10	$85.10
Purchase #3	$232.75	9.607%	$255.1103	$255.11	$255.10	$255.10
Purchase #4	$215.62	8.687%	$234.3509	$234.35	$234.35	$234.40
Purchase #5	$89.56	3.696%	$92.8701	$92.87	$92.85	$92.90
Purchase #6	$56.95	5.219%	$59.9222	$59.92	$59.90	$59.90
Purchase #7	$159.62	5.831%	$168.9274	$168.93	$168.95	$168.90
7 purchase totals =	$1,017.13		$1,105.1706	$1,105.17	$1,105.15	$1,105.20