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	$79.77	7.240%	$85.5453	$85.55	$85.55	$85.50
Purchase #2	$164.73	9.457%	$180.3085	$180.31	$180.30	$180.30
Purchase #3	$85.56	3.834%	$88.8404	$88.84	$88.85	$88.80
Purchase #4	$89.32	9.228%	$97.5624	$97.56	$97.55	$97.60
Purchase #5	$228.77	7.518%	$245.9689	$245.97	$245.95	$246.00
Purchase #6	$154.49	11.861%	$172.8141	$172.81	$172.80	$172.80
Purchase #7	$63.84	11.809%	$71.3789	$71.38	$71.40	$71.40
7 purchase totals =	$866.48		$942.4185	$942.42	$942.40	$942.40