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	$74.77	6.700%	$79.7796	$79.78	$79.80	$79.80
Purchase #2	$234.73	6.178%	$249.2316	$249.23	$249.25	$249.20
Purchase #3	$186.25	12.222%	$209.0135	$209.01	$209.00	$209.00
Purchase #4	$53.85	10.577%	$59.5457	$59.55	$59.55	$59.50
Purchase #5	$114.75	10.615%	$126.9307	$126.93	$126.95	$126.90
Purchase #6	$92.90	10.362%	$102.5263	$102.53	$102.55	$102.50
Purchase #7	$173.88	6.738%	$185.596	$185.60	$185.60	$185.60
7 purchase totals =	$931.13		$1,012.6234	$1,012.63	$1,012.70	$1,012.50