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	$31.61	13.290%	$35.811	$35.81	$35.80	$35.80
Purchase #2	$75.46	4.677%	$78.9893	$78.99	$79.00	$79.00
Purchase #3	$103.70	5.497%	$109.4004	$109.40	$109.40	$109.40
Purchase #4	$146.32	12.687%	$164.8836	$164.88	$164.90	$164.90
Purchase #5	$94.85	9.849%	$104.1918	$104.19	$104.20	$104.20
Purchase #6	$135.53	11.600%	$151.2515	$151.25	$151.25	$151.30
Purchase #7	$158.46	5.614%	$167.3559	$167.36	$167.35	$167.40
7 purchase totals =	$745.93		$811.8835	$811.88	$811.90	$812.00