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	$168.76	6.833%	$180.2914	$180.29	$180.30	$180.30
Purchase #2	$73.78	11.734%	$82.4373	$82.44	$82.45	$82.40
Purchase #3	$218.43	11.440%	$243.4184	$243.42	$243.40	$243.40
Purchase #4	$79.50	4.430%	$83.0219	$83.02	$83.00	$83.00
Purchase #5	$161.41	6.741%	$172.2906	$172.29	$172.30	$172.30
Purchase #6	$219.67	13.678%	$249.7165	$249.72	$249.70	$249.70
Purchase #7	$38.88	4.148%	$40.4927	$40.49	$40.50	$40.50
7 purchase totals =	$960.43		$1,051.6688	$1,051.67	$1,051.65	$1,051.60