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	$89.79	11.771%	$100.3592	$100.36	$100.35	$100.40
Purchase #2	$165.99	12.648%	$186.9844	$186.98	$187.00	$187.00
Purchase #3	$141.41	4.206%	$147.3577	$147.36	$147.35	$147.40
Purchase #4	$114.42	5.325%	$120.5129	$120.51	$120.50	$120.50
Purchase #5	$115.96	6.169%	$123.1136	$123.11	$123.10	$123.10
Purchase #6	$231.90	13.809%	$263.9231	$263.92	$263.90	$263.90
Purchase #7	$199.36	12.146%	$223.5743	$223.57	$223.55	$223.60
7 purchase totals =	$1,058.83		$1,165.8252	$1,165.81	$1,165.75	$1,165.90