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	$83.89	6.200%	$89.0912	$89.09	$89.10	$89.10
Purchase #2	$108.41	11.424%	$120.7948	$120.79	$120.80	$120.80
Purchase #3	$18.80	11.266%	$20.918	$20.92	$20.90	$20.90
Purchase #4	$46.83	11.726%	$52.3213	$52.32	$52.30	$52.30
Purchase #5	$155.69	5.559%	$164.3448	$164.34	$164.35	$164.30
Purchase #6	$161.79	7.614%	$174.1087	$174.11	$174.10	$174.10
Purchase #7	$45.42	5.682%	$48.0008	$48.00	$48.00	$48.00
7 purchase totals =	$620.83		$669.5796	$669.57	$669.55	$669.50