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	$81.25	12.411%	$91.3339	$91.33	$91.35	$91.30
Purchase #2	$192.58	6.472%	$205.0438	$205.04	$205.05	$205.00
Purchase #3	$217.67	12.825%	$245.5862	$245.59	$245.60	$245.60
Purchase #4	$129.68	10.120%	$142.8036	$142.80	$142.80	$142.80
Purchase #5	$57.33	4.457%	$59.8852	$59.89	$59.90	$59.90
Purchase #6	$67.55	6.729%	$72.0954	$72.10	$72.10	$72.10
Purchase #7	$203.74	9.369%	$222.8284	$222.83	$222.85	$222.80
7 purchase totals =	$949.80		$1,039.5765	$1,039.58	$1,039.65	$1,039.50