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	$75.76	9.190%	$82.7223	$82.72	$82.70	$82.70
Purchase #2	$95.97	10.736%	$106.2733	$106.27	$106.25	$106.30
Purchase #3	$139.90	3.122%	$144.2677	$144.27	$144.25	$144.30
Purchase #4	$112.43	12.446%	$126.423	$126.42	$126.40	$126.40
Purchase #5	$59.60	8.290%	$64.5408	$64.54	$64.55	$64.50
Purchase #6	$79.79	10.787%	$88.3969	$88.40	$88.40	$88.40
Purchase #7	$211.91	5.473%	$223.5078	$223.51	$223.50	$223.50
7 purchase totals =	$775.36		$836.1318	$836.13	$836.05	$836.10