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	$133.73	6.766%	$142.7782	$142.78	$142.80	$142.80
Purchase #2	$107.82	3.290%	$111.3673	$111.37	$111.35	$111.40
Purchase #3	$75.29	3.479%	$77.9093	$77.91	$77.90	$77.90
Purchase #4	$106.44	4.591%	$111.3267	$111.33	$111.35	$111.30
Purchase #5	$94.38	13.704%	$107.3138	$107.31	$107.30	$107.30
Purchase #6	$170.88	12.357%	$191.9956	$192.00	$192.00	$192.00
Purchase #7	$168.90	13.789%	$192.1896	$192.19	$192.20	$192.20
7 purchase totals =	$857.44		$934.8805	$934.89	$934.90	$934.90