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	$84.96	5.212%	$89.3881	$89.39	$89.40	$89.40
Purchase #2	$101.48	11.283%	$112.93	$112.93	$112.95	$112.90
Purchase #3	$115.76	13.581%	$131.4814	$131.48	$131.50	$131.50
Purchase #4	$226.28	8.663%	$245.8826	$245.88	$245.90	$245.90
Purchase #5	$144.88	9.781%	$159.0507	$159.05	$159.05	$159.10
Purchase #6	$164.94	12.807%	$186.0639	$186.06	$186.05	$186.10
Purchase #7	$75.71	6.494%	$80.6266	$80.63	$80.65	$80.60
7 purchase totals =	$914.01		$1,005.4233	$1,005.42	$1,005.50	$1,005.50