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	$67.59	4.774%	$70.8167	$70.82	$70.80	$70.80
Purchase #2	$88.90	6.518%	$94.6945	$94.69	$94.70	$94.70
Purchase #3	$214.36	8.710%	$233.0308	$233.03	$233.05	$233.00
Purchase #4	$181.81	11.813%	$203.2872	$203.29	$203.30	$203.30
Purchase #5	$155.61	7.557%	$167.3694	$167.37	$167.35	$167.40
Purchase #6	$85.30	5.523%	$90.0111	$90.01	$90.00	$90.00
Purchase #7	$245.55	4.191%	$255.841	$255.84	$255.85	$255.80
7 purchase totals =	$1,039.12		$1,115.0507	$1,115.05	$1,115.05	$1,115.00