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	$107.81	9.468%	$118.0175	$118.02	$118.00	$118.00
Purchase #2	$94.63	11.794%	$105.7907	$105.79	$105.80	$105.80
Purchase #3	$112.52	12.109%	$126.145	$126.15	$126.15	$126.10
Purchase #4	$35.48	12.406%	$39.8816	$39.88	$39.90	$39.90
Purchase #5	$142.76	11.736%	$159.5143	$159.51	$159.50	$159.50
Purchase #6	$186.94	12.358%	$210.042	$210.04	$210.05	$210.00
Purchase #7	$94.43	4.770%	$98.9343	$98.93	$98.95	$98.90
7 purchase totals =	$774.57		$858.3254	$858.32	$858.35	$858.20