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	$40.94	13.391%	$46.4223	$46.42	$46.40	$46.40
Purchase #2	$113.85	5.322%	$119.9091	$119.91	$119.90	$119.90
Purchase #3	$170.77	4.416%	$178.3112	$178.31	$178.30	$178.30
Purchase #4	$10.31	11.788%	$11.5253	$11.53	$11.55	$11.50
Purchase #5	$178.56	3.863%	$185.4578	$185.46	$185.45	$185.50
Purchase #6	$89.76	11.171%	$99.7871	$99.79	$99.80	$99.80
Purchase #7	$5.38	9.263%	$5.8783	$5.88	$5.90	$5.90
7 purchase totals =	$609.57		$647.2911	$647.30	$647.30	$647.30