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	$92.26	7.122%	$98.8308	$98.83	$98.85	$98.80
Purchase #2	$246.39	11.577%	$274.9146	$274.91	$274.90	$274.90
Purchase #3	$166.43	11.607%	$185.7475	$185.75	$185.75	$185.70
Purchase #4	$10.78	11.849%	$12.0573	$12.06	$12.05	$12.10
Purchase #5	$67.56	13.285%	$76.5353	$76.54	$76.55	$76.50
Purchase #6	$151.88	8.558%	$164.8779	$164.88	$164.90	$164.90
Purchase #7	$191.68	6.316%	$203.7865	$203.79	$203.80	$203.80
7 purchase totals =	$926.98		$1,016.7499	$1,016.76	$1,016.80	$1,016.70