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	$27.88	3.260%	$28.7889	$28.79	$28.80	$28.80
Purchase #2	$88.49	9.712%	$97.0841	$97.08	$97.10	$97.10
Purchase #3	$89.32	6.121%	$94.7873	$94.79	$94.80	$94.80
Purchase #4	$174.83	6.609%	$186.3845	$186.38	$186.40	$186.40
Purchase #5	$90.84	9.552%	$99.517	$99.52	$99.50	$99.50
Purchase #6	$225.80	11.569%	$251.9228	$251.92	$251.90	$251.90
Purchase #7	$94.80	6.353%	$100.8226	$100.82	$100.80	$100.80
7 purchase totals =	$791.96		$859.3072	$859.30	$859.30	$859.30