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	$180.43	3.253%	$186.2994	$186.30	$186.30	$186.30
Purchase #2	$174.65	12.546%	$196.5616	$196.56	$196.55	$196.60
Purchase #3	$82.98	9.572%	$90.9228	$90.92	$90.90	$90.90
Purchase #4	$249.69	10.301%	$275.4106	$275.41	$275.40	$275.40
Purchase #5	$109.25	5.220%	$114.9529	$114.95	$114.95	$115.00
Purchase #6	$162.69	3.177%	$167.8587	$167.86	$167.85	$167.90
Purchase #7	$169.27	3.147%	$174.5969	$174.60	$174.60	$174.60
7 purchase totals =	$1,128.96		$1,206.6029	$1,206.60	$1,206.55	$1,206.70