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	$40.82	11.448%	$45.4931	$45.49	$45.50	$45.50
Purchase #2	$210.33	6.455%	$223.9068	$223.91	$223.90	$223.90
Purchase #3	$168.76	8.608%	$183.2869	$183.29	$183.30	$183.30
Purchase #4	$78.39	12.360%	$88.079	$88.08	$88.10	$88.10
Purchase #5	$128.81	8.365%	$139.585	$139.59	$139.60	$139.60
Purchase #6	$128.40	11.136%	$142.6986	$142.70	$142.70	$142.70
Purchase #7	$167.54	6.473%	$178.3849	$178.38	$178.40	$178.40
7 purchase totals =	$923.05		$1,001.4343	$1,001.44	$1,001.50	$1,001.50