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	$110.67	12.219%	$124.1928	$124.19	$124.20	$124.20
Purchase #2	$52.94	8.426%	$57.4007	$57.40	$57.40	$57.40
Purchase #3	$126.53	3.222%	$130.6068	$130.61	$130.60	$130.60
Purchase #4	$165.27	3.530%	$171.104	$171.10	$171.10	$171.10
Purchase #5	$193.89	11.360%	$215.9159	$215.92	$215.90	$215.90
Purchase #6	$167.86	6.270%	$178.3848	$178.38	$178.40	$178.40
Purchase #7	$171.61	7.128%	$183.8424	$183.84	$183.85	$183.80
7 purchase totals =	$988.77		$1,061.4474	$1,061.44	$1,061.45	$1,061.40