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	$189.52	12.645%	$213.4848	$213.48	$213.50	$213.50
Purchase #2	$64.58	12.607%	$72.7216	$72.72	$72.70	$72.70
Purchase #3	$124.48	3.677%	$129.0571	$129.06	$129.05	$129.10
Purchase #4	$57.88	3.168%	$59.7136	$59.71	$59.70	$59.70
Purchase #5	$150.48	10.219%	$165.8576	$165.86	$165.85	$165.90
Purchase #6	$16.53	5.700%	$17.4722	$17.47	$17.45	$17.50
Purchase #7	$246.54	9.167%	$269.1403	$269.14	$269.15	$269.10
7 purchase totals =	$850.01		$927.4472	$927.44	$927.40	$927.50