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	$38.81	8.779%	$42.2171	$42.22	$42.20	$42.20
Purchase #2	$38.86	8.774%	$42.2696	$42.27	$42.25	$42.30
Purchase #3	$157.57	8.111%	$170.3505	$170.35	$170.35	$170.40
Purchase #4	$169.85	7.280%	$182.2151	$182.22	$182.20	$182.20
Purchase #5	$127.65	11.250%	$142.0106	$142.01	$142.00	$142.00
Purchase #6	$85.90	3.735%	$89.1084	$89.11	$89.10	$89.10
Purchase #7	$219.99	5.537%	$232.1708	$232.17	$232.15	$232.20
7 purchase totals =	$838.63		$900.3421	$900.35	$900.25	$900.40