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	$247.40	11.758%	$276.4893	$276.49	$276.50	$276.50
Purchase #2	$211.37	5.518%	$223.0334	$223.03	$223.05	$223.00
Purchase #3	$119.33	10.533%	$131.899	$131.90	$131.90	$131.90
Purchase #4	$84.71	7.796%	$91.314	$91.31	$91.30	$91.30
Purchase #5	$215.30	6.415%	$229.1115	$229.11	$229.10	$229.10
Purchase #6	$80.60	6.212%	$85.6069	$85.61	$85.60	$85.60
Purchase #7	$194.67	9.614%	$213.3856	$213.39	$213.40	$213.40
7 purchase totals =	$1,153.38		$1,250.8397	$1,250.84	$1,250.85	$1,250.80